diff --git a/notebooks/debugging.ipynb b/notebooks/debugging.ipynb
new file mode 100644
index 0000000..9532296
--- /dev/null
+++ b/notebooks/debugging.ipynb
@@ -0,0 +1,1227 @@
+{
+ "cells": [
+  {
+   "cell_type": "code",
+   "execution_count": 2,
+   "metadata": {},
+   "outputs": [],
+   "source": [
+    "import pickle\n",
+    "import numpy as np\n",
+    "import pandas as pd"
+   ]
+  },
+  {
+   "cell_type": "code",
+   "execution_count": 4,
+   "metadata": {},
+   "outputs": [],
+   "source": [
+    "def pkload(path):\n",
+    "    with open(path, 'rb') as f:\n",
+    "        obj = pickle.load(f)\n",
+    "    return obj"
+   ]
+  },
+  {
+   "cell_type": "markdown",
+   "metadata": {},
+   "source": [
+    "Searching for journeys from Uster, Gschwader (stop 8588052) to Buchs ZH, Furttalstrasse (stop 8595356) with arrival at 17:30 leads to a footpath of over 3.2km + in reality, while the algorithm prints this:\n",
+    "\n",
+    "\" Walk 2.1 minutes from Birmensdorf ZH (stop 8502221)\n",
+    "        to Dällikon, Industrie (stop 8576276)\""
+   ]
+  },
+  {
+   "cell_type": "code",
+   "execution_count": 54,
+   "metadata": {},
+   "outputs": [
+    {
+     "data": {
+      "text/html": [
+       "<div>\n",
+       "<style scoped>\n",
+       "    .dataframe tbody tr th:only-of-type {\n",
+       "        vertical-align: middle;\n",
+       "    }\n",
+       "\n",
+       "    .dataframe tbody tr th {\n",
+       "        vertical-align: top;\n",
+       "    }\n",
+       "\n",
+       "    .dataframe thead th {\n",
+       "        text-align: right;\n",
+       "    }\n",
+       "</style>\n",
+       "<table border=\"1\" class=\"dataframe\">\n",
+       "  <thead>\n",
+       "    <tr style=\"text-align: right;\">\n",
+       "      <th></th>\n",
+       "      <th>index</th>\n",
+       "      <th>route_id</th>\n",
+       "      <th>stop_id_general</th>\n",
+       "      <th>trip_id</th>\n",
+       "      <th>stop_id</th>\n",
+       "      <th>arrival_time</th>\n",
+       "      <th>departure_time</th>\n",
+       "      <th>stop_sequence</th>\n",
+       "      <th>stop_name</th>\n",
+       "      <th>stop_lat</th>\n",
+       "      <th>stop_lon</th>\n",
+       "      <th>trip_headsign</th>\n",
+       "      <th>trip_short_name</th>\n",
+       "      <th>direction_id</th>\n",
+       "      <th>departure_first_stop</th>\n",
+       "      <th>route_int</th>\n",
+       "      <th>stop_count</th>\n",
+       "      <th>stop_int</th>\n",
+       "      <th>route_desc</th>\n",
+       "      <th>monotonically_increasing_id</th>\n",
+       "    </tr>\n",
+       "  </thead>\n",
+       "  <tbody>\n",
+       "    <tr>\n",
+       "      <th>27708</th>\n",
+       "      <td>197013</td>\n",
+       "      <td>26-5-A-j19-1</td>\n",
+       "      <td>8502221</td>\n",
+       "      <td>114.TA.26-5-A-j19-1.37.R</td>\n",
+       "      <td>8502221:0:2</td>\n",
+       "      <td>2020-05-24 19:35:00</td>\n",
+       "      <td>2020-05-24 19:35:00</td>\n",
+       "      <td>9</td>\n",
+       "      <td>Birmensdorf ZH</td>\n",
+       "      <td>47.357496</td>\n",
+       "      <td>8.437543</td>\n",
+       "      <td>Pfäffikon SZ</td>\n",
+       "      <td>18575</td>\n",
+       "      <td>1</td>\n",
+       "      <td>19:22:00</td>\n",
+       "      <td>149</td>\n",
+       "      <td>10</td>\n",
+       "      <td>276</td>\n",
+       "      <td>S-Bahn</td>\n",
+       "      <td>180388626589</td>\n",
+       "    </tr>\n",
+       "  </tbody>\n",
+       "</table>\n",
+       "</div>"
+      ],
+      "text/plain": [
+       "        index      route_id  stop_id_general                   trip_id  \\\n",
+       "27708  197013  26-5-A-j19-1          8502221  114.TA.26-5-A-j19-1.37.R   \n",
+       "\n",
+       "           stop_id        arrival_time      departure_time  stop_sequence  \\\n",
+       "27708  8502221:0:2 2020-05-24 19:35:00 2020-05-24 19:35:00              9   \n",
+       "\n",
+       "            stop_name   stop_lat  stop_lon trip_headsign  trip_short_name  \\\n",
+       "27708  Birmensdorf ZH  47.357496  8.437543  Pfäffikon SZ            18575   \n",
+       "\n",
+       "       direction_id departure_first_stop  route_int  stop_count  stop_int  \\\n",
+       "27708             1             19:22:00        149          10       276   \n",
+       "\n",
+       "      route_desc  monotonically_increasing_id  \n",
+       "27708     S-Bahn                 180388626589  "
+      ]
+     },
+     "execution_count": 54,
+     "metadata": {},
+     "output_type": "execute_result"
+    }
+   ],
+   "source": [
+    "# Birmensdorf ZH\n",
+    "stop_times = pkload(\"../data/stop_times_df_cyril.pkl\")\n",
+    "stop_times[stop_times['stop_id_general']==8502221].head(1)"
+   ]
+  },
+  {
+   "cell_type": "code",
+   "execution_count": 55,
+   "metadata": {},
+   "outputs": [
+    {
+     "data": {
+      "text/html": [
+       "<div>\n",
+       "<style scoped>\n",
+       "    .dataframe tbody tr th:only-of-type {\n",
+       "        vertical-align: middle;\n",
+       "    }\n",
+       "\n",
+       "    .dataframe tbody tr th {\n",
+       "        vertical-align: top;\n",
+       "    }\n",
+       "\n",
+       "    .dataframe thead th {\n",
+       "        text-align: right;\n",
+       "    }\n",
+       "</style>\n",
+       "<table border=\"1\" class=\"dataframe\">\n",
+       "  <thead>\n",
+       "    <tr style=\"text-align: right;\">\n",
+       "      <th></th>\n",
+       "      <th>index</th>\n",
+       "      <th>route_id</th>\n",
+       "      <th>stop_id_general</th>\n",
+       "      <th>trip_id</th>\n",
+       "      <th>stop_id</th>\n",
+       "      <th>arrival_time</th>\n",
+       "      <th>departure_time</th>\n",
+       "      <th>stop_sequence</th>\n",
+       "      <th>stop_name</th>\n",
+       "      <th>stop_lat</th>\n",
+       "      <th>stop_lon</th>\n",
+       "      <th>trip_headsign</th>\n",
+       "      <th>trip_short_name</th>\n",
+       "      <th>direction_id</th>\n",
+       "      <th>departure_first_stop</th>\n",
+       "      <th>route_int</th>\n",
+       "      <th>stop_count</th>\n",
+       "      <th>stop_int</th>\n",
+       "      <th>route_desc</th>\n",
+       "      <th>monotonically_increasing_id</th>\n",
+       "    </tr>\n",
+       "  </thead>\n",
+       "  <tbody>\n",
+       "    <tr>\n",
+       "      <th>1935</th>\n",
+       "      <td>222352</td>\n",
+       "      <td>26-449-j19-1</td>\n",
+       "      <td>8576276</td>\n",
+       "      <td>17.TA.26-449-j19-1.1.H</td>\n",
+       "      <td>8576276</td>\n",
+       "      <td>NaT</td>\n",
+       "      <td>2020-05-24 07:00:00</td>\n",
+       "      <td>2</td>\n",
+       "      <td>Dällikon, Industrie</td>\n",
+       "      <td>47.444737</td>\n",
+       "      <td>8.438783</td>\n",
+       "      <td>Buchs-Dällikon, Bahnhof</td>\n",
+       "      <td>4747</td>\n",
+       "      <td>0</td>\n",
+       "      <td>07:00:00</td>\n",
+       "      <td>19</td>\n",
+       "      <td>3</td>\n",
+       "      <td>474</td>\n",
+       "      <td>Bus</td>\n",
+       "      <td>8589935205</td>\n",
+       "    </tr>\n",
+       "  </tbody>\n",
+       "</table>\n",
+       "</div>"
+      ],
+      "text/plain": [
+       "       index      route_id  stop_id_general                 trip_id  stop_id  \\\n",
+       "1935  222352  26-449-j19-1          8576276  17.TA.26-449-j19-1.1.H  8576276   \n",
+       "\n",
+       "     arrival_time      departure_time  stop_sequence            stop_name  \\\n",
+       "1935          NaT 2020-05-24 07:00:00              2  Dällikon, Industrie   \n",
+       "\n",
+       "       stop_lat  stop_lon            trip_headsign  trip_short_name  \\\n",
+       "1935  47.444737  8.438783  Buchs-Dällikon, Bahnhof             4747   \n",
+       "\n",
+       "      direction_id departure_first_stop  route_int  stop_count  stop_int  \\\n",
+       "1935             0             07:00:00         19           3       474   \n",
+       "\n",
+       "     route_desc  monotonically_increasing_id  \n",
+       "1935        Bus                   8589935205  "
+      ]
+     },
+     "execution_count": 55,
+     "metadata": {},
+     "output_type": "execute_result"
+    }
+   ],
+   "source": [
+    "# Dallikon Industrie\n",
+    "stop_times[stop_times['stop_id_general']==8576276].head(1)"
+   ]
+  },
+  {
+   "cell_type": "markdown",
+   "metadata": {},
+   "source": [
+    "A google maps footpaths using GPS coordinates yields a walk of 14.1 km. Is there a footpath defined between those two stops in transfers ?"
+   ]
+  },
+  {
+   "cell_type": "code",
+   "execution_count": 56,
+   "metadata": {},
+   "outputs": [],
+   "source": [
+    "transfers = pkload(\"../data/transfer_df_cyril.pkl\")"
+   ]
+  },
+  {
+   "cell_type": "code",
+   "execution_count": 58,
+   "metadata": {},
+   "outputs": [
+    {
+     "data": {
+      "text/html": [
+       "<div>\n",
+       "<style scoped>\n",
+       "    .dataframe tbody tr th:only-of-type {\n",
+       "        vertical-align: middle;\n",
+       "    }\n",
+       "\n",
+       "    .dataframe tbody tr th {\n",
+       "        vertical-align: top;\n",
+       "    }\n",
+       "\n",
+       "    .dataframe thead th {\n",
+       "        text-align: right;\n",
+       "    }\n",
+       "</style>\n",
+       "<table border=\"1\" class=\"dataframe\">\n",
+       "  <thead>\n",
+       "    <tr style=\"text-align: right;\">\n",
+       "      <th></th>\n",
+       "      <th>index</th>\n",
+       "      <th>stop_id_general</th>\n",
+       "      <th>stop_int</th>\n",
+       "      <th>stop_lat_first</th>\n",
+       "      <th>stop_lon_first</th>\n",
+       "      <th>stop_name_first</th>\n",
+       "      <th>stop_id_general_2</th>\n",
+       "      <th>stop_int_2</th>\n",
+       "      <th>stop_lat_first_2</th>\n",
+       "      <th>stop_lon_first_2</th>\n",
+       "      <th>stop_name_first_2</th>\n",
+       "      <th>distance</th>\n",
+       "      <th>walking_time</th>\n",
+       "      <th>monotonically_increasing_id</th>\n",
+       "    </tr>\n",
+       "  </thead>\n",
+       "  <tbody>\n",
+       "    <tr>\n",
+       "      <th>1300</th>\n",
+       "      <td>3887</td>\n",
+       "      <td>8502221</td>\n",
+       "      <td>276</td>\n",
+       "      <td>47.357557</td>\n",
+       "      <td>8.437543</td>\n",
+       "      <td>Birmensdorf ZH</td>\n",
+       "      <td>8573718</td>\n",
+       "      <td>473</td>\n",
+       "      <td>47.357125</td>\n",
+       "      <td>8.438801</td>\n",
+       "      <td>Birmensdorf ZH, Bahnhof</td>\n",
+       "      <td>0.106219</td>\n",
+       "      <td>127</td>\n",
+       "      <td>352187318287</td>\n",
+       "    </tr>\n",
+       "    <tr>\n",
+       "      <th>1301</th>\n",
+       "      <td>3888</td>\n",
+       "      <td>8502221</td>\n",
+       "      <td>276</td>\n",
+       "      <td>47.357557</td>\n",
+       "      <td>8.437543</td>\n",
+       "      <td>Birmensdorf ZH</td>\n",
+       "      <td>8502950</td>\n",
+       "      <td>877</td>\n",
+       "      <td>47.353936</td>\n",
+       "      <td>8.437175</td>\n",
+       "      <td>Birmensdorf ZH, Zentrum</td>\n",
+       "      <td>0.403584</td>\n",
+       "      <td>484</td>\n",
+       "      <td>352187318288</td>\n",
+       "    </tr>\n",
+       "    <tr>\n",
+       "      <th>1302</th>\n",
+       "      <td>3889</td>\n",
+       "      <td>8502221</td>\n",
+       "      <td>276</td>\n",
+       "      <td>47.357557</td>\n",
+       "      <td>8.437543</td>\n",
+       "      <td>Birmensdorf ZH</td>\n",
+       "      <td>8583870</td>\n",
+       "      <td>1154</td>\n",
+       "      <td>47.357234</td>\n",
+       "      <td>8.437013</td>\n",
+       "      <td>Birmensdorf ZH, Bahnhof Süd</td>\n",
+       "      <td>0.053666</td>\n",
+       "      <td>64</td>\n",
+       "      <td>352187318289</td>\n",
+       "    </tr>\n",
+       "  </tbody>\n",
+       "</table>\n",
+       "</div>"
+      ],
+      "text/plain": [
+       "      index  stop_id_general  stop_int  stop_lat_first  stop_lon_first  \\\n",
+       "1300   3887          8502221       276       47.357557        8.437543   \n",
+       "1301   3888          8502221       276       47.357557        8.437543   \n",
+       "1302   3889          8502221       276       47.357557        8.437543   \n",
+       "\n",
+       "     stop_name_first  stop_id_general_2  stop_int_2  stop_lat_first_2  \\\n",
+       "1300  Birmensdorf ZH            8573718         473         47.357125   \n",
+       "1301  Birmensdorf ZH            8502950         877         47.353936   \n",
+       "1302  Birmensdorf ZH            8583870        1154         47.357234   \n",
+       "\n",
+       "      stop_lon_first_2            stop_name_first_2  distance  walking_time  \\\n",
+       "1300          8.438801      Birmensdorf ZH, Bahnhof  0.106219           127   \n",
+       "1301          8.437175      Birmensdorf ZH, Zentrum  0.403584           484   \n",
+       "1302          8.437013  Birmensdorf ZH, Bahnhof Süd  0.053666            64   \n",
+       "\n",
+       "      monotonically_increasing_id  \n",
+       "1300                 352187318287  \n",
+       "1301                 352187318288  \n",
+       "1302                 352187318289  "
+      ]
+     },
+     "execution_count": 58,
+     "metadata": {},
+     "output_type": "execute_result"
+    }
+   ],
+   "source": [
+    "# transfers from Birmensdorf ZH\n",
+    "transfers[transfers['stop_id_general']==8502221]"
+   ]
+  },
+  {
+   "cell_type": "code",
+   "execution_count": 60,
+   "metadata": {},
+   "outputs": [],
+   "source": [
+    "# Transfers from Dallikon Industrie"
+   ]
+  },
+  {
+   "cell_type": "code",
+   "execution_count": 59,
+   "metadata": {},
+   "outputs": [
+    {
+     "data": {
+      "text/html": [
+       "<div>\n",
+       "<style scoped>\n",
+       "    .dataframe tbody tr th:only-of-type {\n",
+       "        vertical-align: middle;\n",
+       "    }\n",
+       "\n",
+       "    .dataframe tbody tr th {\n",
+       "        vertical-align: top;\n",
+       "    }\n",
+       "\n",
+       "    .dataframe thead th {\n",
+       "        text-align: right;\n",
+       "    }\n",
+       "</style>\n",
+       "<table border=\"1\" class=\"dataframe\">\n",
+       "  <thead>\n",
+       "    <tr style=\"text-align: right;\">\n",
+       "      <th></th>\n",
+       "      <th>index</th>\n",
+       "      <th>stop_id_general</th>\n",
+       "      <th>stop_int</th>\n",
+       "      <th>stop_lat_first</th>\n",
+       "      <th>stop_lon_first</th>\n",
+       "      <th>stop_name_first</th>\n",
+       "      <th>stop_id_general_2</th>\n",
+       "      <th>stop_int_2</th>\n",
+       "      <th>stop_lat_first_2</th>\n",
+       "      <th>stop_lon_first_2</th>\n",
+       "      <th>stop_name_first_2</th>\n",
+       "      <th>distance</th>\n",
+       "      <th>walking_time</th>\n",
+       "      <th>monotonically_increasing_id</th>\n",
+       "    </tr>\n",
+       "  </thead>\n",
+       "  <tbody>\n",
+       "  </tbody>\n",
+       "</table>\n",
+       "</div>"
+      ],
+      "text/plain": [
+       "Empty DataFrame\n",
+       "Columns: [index, stop_id_general, stop_int, stop_lat_first, stop_lon_first, stop_name_first, stop_id_general_2, stop_int_2, stop_lat_first_2, stop_lon_first_2, stop_name_first_2, distance, walking_time, monotonically_increasing_id]\n",
+       "Index: []"
+      ]
+     },
+     "execution_count": 59,
+     "metadata": {},
+     "output_type": "execute_result"
+    }
+   ],
+   "source": [
+    "transfers[transfers['stop_id_general']==8576276]"
+   ]
+  },
+  {
+   "cell_type": "markdown",
+   "metadata": {},
+   "source": [
+    "There are no footpaths between Birmensdorf ZH and Dallikon Industrie, and interestingly, Dallikon Industrie has no footpaths at all. That points to a bug with the gestion of 'None' pointers in the array stops for footpaths"
+   ]
+  },
+  {
+   "cell_type": "code",
+   "execution_count": 61,
+   "metadata": {},
+   "outputs": [],
+   "source": [
+    "transfer_array = pkload(\"../data/transfer_array_cyril.pkl\")\n",
+    "stops =  pkload(\"../data/stops_array_cyril.pkl\")"
+   ]
+  },
+  {
+   "cell_type": "code",
+   "execution_count": 64,
+   "metadata": {},
+   "outputs": [
+    {
+     "data": {
+      "text/plain": [
+       "array([[3075, 1297.0],\n",
+       "       [3119, 1300.0],\n",
+       "       [3131, 1303.0]], dtype=object)"
+      ]
+     },
+     "execution_count": 64,
+     "metadata": {},
+     "output_type": "execute_result"
+    }
+   ],
+   "source": [
+    "# transfers from Birmensdorf ZH\n",
+    "stop_int = 276\n",
+    "stops[stop_int-1:stop_int+2]"
+   ]
+  },
+  {
+   "cell_type": "code",
+   "execution_count": 65,
+   "metadata": {},
+   "outputs": [
+    {
+     "data": {
+      "text/plain": [
+       "array([[ 473,  127],\n",
+       "       [ 877,  484],\n",
+       "       [1154,   64]])"
+      ]
+     },
+     "execution_count": 65,
+     "metadata": {},
+     "output_type": "execute_result"
+    }
+   ],
+   "source": [
+    "transfer_array[int(stops[stop_int][1]):int(stops[stop_int+1][1])]"
+   ]
+  },
+  {
+   "cell_type": "markdown",
+   "metadata": {},
+   "source": [
+    "**The first entry of transfer_array[276] corresponding to Birmensdorf ZH is 473, which is one less than 474, the stop_id of Dallikon Industrie**. That may be a clue to what's going wrong with the algorithm."
+   ]
+  },
+  {
+   "cell_type": "code",
+   "execution_count": 66,
+   "metadata": {},
+   "outputs": [
+    {
+     "data": {
+      "text/plain": [
+       "array([[5408, 2157.0],\n",
+       "       [5417, nan],\n",
+       "       [5420, 2160.0]], dtype=object)"
+      ]
+     },
+     "execution_count": 66,
+     "metadata": {},
+     "output_type": "execute_result"
+    }
+   ],
+   "source": [
+    "# transfers from Dallikon Industrie\n",
+    "stop_int = 474\n",
+    "stops[stop_int-1:stop_int+2]\n"
+   ]
+  },
+  {
+   "cell_type": "code",
+   "execution_count": 69,
+   "metadata": {},
+   "outputs": [
+    {
+     "ename": "ValueError",
+     "evalue": "cannot convert float NaN to integer",
+     "output_type": "error",
+     "traceback": [
+      "\u001b[0;31m---------------------------------------------------------------------------\u001b[0m",
+      "\u001b[0;31mValueError\u001b[0m                                Traceback (most recent call last)",
+      "\u001b[0;32m<ipython-input-69-28a210e2fa85>\u001b[0m in \u001b[0;36m<module>\u001b[0;34m\u001b[0m\n\u001b[1;32m      1\u001b[0m \u001b[0;31m# Trying to access the transfer for the nan pointer (SHOULD FAIL)\u001b[0m\u001b[0;34m\u001b[0m\u001b[0;34m\u001b[0m\u001b[0;34m\u001b[0m\u001b[0m\n\u001b[0;32m----> 2\u001b[0;31m \u001b[0mtransfer_array\u001b[0m\u001b[0;34m[\u001b[0m\u001b[0mint\u001b[0m\u001b[0;34m(\u001b[0m\u001b[0mstops\u001b[0m\u001b[0;34m[\u001b[0m\u001b[0mstop_int\u001b[0m\u001b[0;34m]\u001b[0m\u001b[0;34m[\u001b[0m\u001b[0;36m1\u001b[0m\u001b[0;34m]\u001b[0m\u001b[0;34m)\u001b[0m\u001b[0;34m:\u001b[0m\u001b[0mint\u001b[0m\u001b[0;34m(\u001b[0m\u001b[0mstops\u001b[0m\u001b[0;34m[\u001b[0m\u001b[0mstop_int\u001b[0m\u001b[0;34m+\u001b[0m\u001b[0;36m1\u001b[0m\u001b[0;34m]\u001b[0m\u001b[0;34m[\u001b[0m\u001b[0;36m1\u001b[0m\u001b[0;34m]\u001b[0m\u001b[0;34m)\u001b[0m\u001b[0;34m]\u001b[0m\u001b[0;34m\u001b[0m\u001b[0;34m\u001b[0m\u001b[0m\n\u001b[0m",
+      "\u001b[0;31mValueError\u001b[0m: cannot convert float NaN to integer"
+     ]
+    }
+   ],
+   "source": [
+    "# Trying to access the transfer for the nan pointer (SHOULD FAIL)\n",
+    "transfer_array[int(stops[stop_int][1]):int(stops[stop_int+1][1])]"
+   ]
+  },
+  {
+   "cell_type": "code",
+   "execution_count": 70,
+   "metadata": {},
+   "outputs": [],
+   "source": [
+    "# checking out what's around the nan pointer:"
+   ]
+  },
+  {
+   "cell_type": "code",
+   "execution_count": 71,
+   "metadata": {},
+   "outputs": [
+    {
+     "data": {
+      "text/plain": [
+       "array([[ 276,  127],\n",
+       "       [ 877,  450],\n",
+       "       [1154,  162]])"
+      ]
+     },
+     "execution_count": 71,
+     "metadata": {},
+     "output_type": "execute_result"
+    }
+   ],
+   "source": [
+    "transfer_array[int(stops[stop_int-1][1]):int(stops[stop_int+1][1])]"
+   ]
+  },
+  {
+   "cell_type": "markdown",
+   "metadata": {},
+   "source": [
+    "The first entry of transfer_array[stop_int-1] is 276, the stop_int of Birmensdorf ZH. However, that is unlikely to be the source of the problem as we are walking from 276 to 474, and thus accessing transfer_array through stops[276][1]."
+   ]
+  },
+  {
+   "cell_type": "markdown",
+   "metadata": {},
+   "source": [
+    "## recapitulating the bug with another journey\n",
+    "\n",
+    "Searching for journeys from Dübendorf, Branzenäsch (stop 8590551) to Kloten, Weinbergstrasse (stop 8579967) with arrival at 17:30 gives an impossible first walk from Dübendorf, Branzenäsch to Uetliberg (stop 8503057)."
+   ]
+  },
+  {
+   "cell_type": "code",
+   "execution_count": 72,
+   "metadata": {},
+   "outputs": [
+    {
+     "data": {
+      "text/html": [
+       "<div>\n",
+       "<style scoped>\n",
+       "    .dataframe tbody tr th:only-of-type {\n",
+       "        vertical-align: middle;\n",
+       "    }\n",
+       "\n",
+       "    .dataframe tbody tr th {\n",
+       "        vertical-align: top;\n",
+       "    }\n",
+       "\n",
+       "    .dataframe thead th {\n",
+       "        text-align: right;\n",
+       "    }\n",
+       "</style>\n",
+       "<table border=\"1\" class=\"dataframe\">\n",
+       "  <thead>\n",
+       "    <tr style=\"text-align: right;\">\n",
+       "      <th></th>\n",
+       "      <th>index</th>\n",
+       "      <th>route_id</th>\n",
+       "      <th>stop_id_general</th>\n",
+       "      <th>trip_id</th>\n",
+       "      <th>stop_id</th>\n",
+       "      <th>arrival_time</th>\n",
+       "      <th>departure_time</th>\n",
+       "      <th>stop_sequence</th>\n",
+       "      <th>stop_name</th>\n",
+       "      <th>stop_lat</th>\n",
+       "      <th>stop_lon</th>\n",
+       "      <th>trip_headsign</th>\n",
+       "      <th>trip_short_name</th>\n",
+       "      <th>direction_id</th>\n",
+       "      <th>departure_first_stop</th>\n",
+       "      <th>route_int</th>\n",
+       "      <th>stop_count</th>\n",
+       "      <th>stop_int</th>\n",
+       "      <th>route_desc</th>\n",
+       "      <th>monotonically_increasing_id</th>\n",
+       "    </tr>\n",
+       "  </thead>\n",
+       "  <tbody>\n",
+       "    <tr>\n",
+       "      <th>95873</th>\n",
+       "      <td>110350</td>\n",
+       "      <td>26-752-j19-1</td>\n",
+       "      <td>8590551</td>\n",
+       "      <td>190.TA.26-752-j19-1.4.R</td>\n",
+       "      <td>8590551</td>\n",
+       "      <td>2020-05-24 07:16:00</td>\n",
+       "      <td>2020-05-24 07:16:00</td>\n",
+       "      <td>11</td>\n",
+       "      <td>Dübendorf, Branzenäsch</td>\n",
+       "      <td>47.394665</td>\n",
+       "      <td>8.631157</td>\n",
+       "      <td>Dübendorf, Kunsteisbahn</td>\n",
+       "      <td>1420</td>\n",
+       "      <td>1</td>\n",
+       "      <td>07:06:00</td>\n",
+       "      <td>563</td>\n",
+       "      <td>15</td>\n",
+       "      <td>503</td>\n",
+       "      <td>Bus</td>\n",
+       "      <td>627065226053</td>\n",
+       "    </tr>\n",
+       "  </tbody>\n",
+       "</table>\n",
+       "</div>"
+      ],
+      "text/plain": [
+       "        index      route_id  stop_id_general                  trip_id  \\\n",
+       "95873  110350  26-752-j19-1          8590551  190.TA.26-752-j19-1.4.R   \n",
+       "\n",
+       "       stop_id        arrival_time      departure_time  stop_sequence  \\\n",
+       "95873  8590551 2020-05-24 07:16:00 2020-05-24 07:16:00             11   \n",
+       "\n",
+       "                    stop_name   stop_lat  stop_lon            trip_headsign  \\\n",
+       "95873  Dübendorf, Branzenäsch  47.394665  8.631157  Dübendorf, Kunsteisbahn   \n",
+       "\n",
+       "       trip_short_name  direction_id departure_first_stop  route_int  \\\n",
+       "95873             1420             1             07:06:00        563   \n",
+       "\n",
+       "       stop_count  stop_int route_desc  monotonically_increasing_id  \n",
+       "95873          15       503        Bus                 627065226053  "
+      ]
+     },
+     "execution_count": 72,
+     "metadata": {},
+     "output_type": "execute_result"
+    }
+   ],
+   "source": [
+    "# Dübendorf, Branzenäsch\n",
+    "stop_times[stop_times['stop_id_general']== 8590551].head(1)"
+   ]
+  },
+  {
+   "cell_type": "code",
+   "execution_count": 73,
+   "metadata": {},
+   "outputs": [
+    {
+     "data": {
+      "text/html": [
+       "<div>\n",
+       "<style scoped>\n",
+       "    .dataframe tbody tr th:only-of-type {\n",
+       "        vertical-align: middle;\n",
+       "    }\n",
+       "\n",
+       "    .dataframe tbody tr th {\n",
+       "        vertical-align: top;\n",
+       "    }\n",
+       "\n",
+       "    .dataframe thead th {\n",
+       "        text-align: right;\n",
+       "    }\n",
+       "</style>\n",
+       "<table border=\"1\" class=\"dataframe\">\n",
+       "  <thead>\n",
+       "    <tr style=\"text-align: right;\">\n",
+       "      <th></th>\n",
+       "      <th>index</th>\n",
+       "      <th>route_id</th>\n",
+       "      <th>stop_id_general</th>\n",
+       "      <th>trip_id</th>\n",
+       "      <th>stop_id</th>\n",
+       "      <th>arrival_time</th>\n",
+       "      <th>departure_time</th>\n",
+       "      <th>stop_sequence</th>\n",
+       "      <th>stop_name</th>\n",
+       "      <th>stop_lat</th>\n",
+       "      <th>stop_lon</th>\n",
+       "      <th>trip_headsign</th>\n",
+       "      <th>trip_short_name</th>\n",
+       "      <th>direction_id</th>\n",
+       "      <th>departure_first_stop</th>\n",
+       "      <th>route_int</th>\n",
+       "      <th>stop_count</th>\n",
+       "      <th>stop_int</th>\n",
+       "      <th>route_desc</th>\n",
+       "      <th>monotonically_increasing_id</th>\n",
+       "    </tr>\n",
+       "  </thead>\n",
+       "  <tbody>\n",
+       "    <tr>\n",
+       "      <th>5304</th>\n",
+       "      <td>51749</td>\n",
+       "      <td>26-10-B-j19-1</td>\n",
+       "      <td>8503057</td>\n",
+       "      <td>181.TA.26-10-B-j19-1.9.H</td>\n",
+       "      <td>8503057</td>\n",
+       "      <td>2020-05-24 07:14:00</td>\n",
+       "      <td>NaT</td>\n",
+       "      <td>8</td>\n",
+       "      <td>Uetliberg</td>\n",
+       "      <td>47.352366</td>\n",
+       "      <td>8.487651</td>\n",
+       "      <td>Uetliberg</td>\n",
+       "      <td>23511</td>\n",
+       "      <td>0</td>\n",
+       "      <td>07:03:00</td>\n",
+       "      <td>62</td>\n",
+       "      <td>4</td>\n",
+       "      <td>415</td>\n",
+       "      <td>S-Bahn</td>\n",
+       "      <td>25769805095</td>\n",
+       "    </tr>\n",
+       "  </tbody>\n",
+       "</table>\n",
+       "</div>"
+      ],
+      "text/plain": [
+       "      index       route_id  stop_id_general                   trip_id  \\\n",
+       "5304  51749  26-10-B-j19-1          8503057  181.TA.26-10-B-j19-1.9.H   \n",
+       "\n",
+       "      stop_id        arrival_time departure_time  stop_sequence  stop_name  \\\n",
+       "5304  8503057 2020-05-24 07:14:00            NaT              8  Uetliberg   \n",
+       "\n",
+       "       stop_lat  stop_lon trip_headsign  trip_short_name  direction_id  \\\n",
+       "5304  47.352366  8.487651     Uetliberg            23511             0   \n",
+       "\n",
+       "     departure_first_stop  route_int  stop_count  stop_int route_desc  \\\n",
+       "5304             07:03:00         62           4       415     S-Bahn   \n",
+       "\n",
+       "      monotonically_increasing_id  \n",
+       "5304                  25769805095  "
+      ]
+     },
+     "execution_count": 73,
+     "metadata": {},
+     "output_type": "execute_result"
+    }
+   ],
+   "source": [
+    "#  Uetliberg (stop 8503057)\n",
+    "stop_times[stop_times['stop_id_general']== 8503057].head(1)"
+   ]
+  },
+  {
+   "cell_type": "markdown",
+   "metadata": {},
+   "source": [
+    "A google maps search for footpaths between the coordinates yields a 14.5 km walk."
+   ]
+  },
+  {
+   "cell_type": "code",
+   "execution_count": 74,
+   "metadata": {},
+   "outputs": [
+    {
+     "data": {
+      "text/html": [
+       "<div>\n",
+       "<style scoped>\n",
+       "    .dataframe tbody tr th:only-of-type {\n",
+       "        vertical-align: middle;\n",
+       "    }\n",
+       "\n",
+       "    .dataframe tbody tr th {\n",
+       "        vertical-align: top;\n",
+       "    }\n",
+       "\n",
+       "    .dataframe thead th {\n",
+       "        text-align: right;\n",
+       "    }\n",
+       "</style>\n",
+       "<table border=\"1\" class=\"dataframe\">\n",
+       "  <thead>\n",
+       "    <tr style=\"text-align: right;\">\n",
+       "      <th></th>\n",
+       "      <th>index</th>\n",
+       "      <th>stop_id_general</th>\n",
+       "      <th>stop_int</th>\n",
+       "      <th>stop_lat_first</th>\n",
+       "      <th>stop_lon_first</th>\n",
+       "      <th>stop_name_first</th>\n",
+       "      <th>stop_id_general_2</th>\n",
+       "      <th>stop_int_2</th>\n",
+       "      <th>stop_lat_first_2</th>\n",
+       "      <th>stop_lon_first_2</th>\n",
+       "      <th>stop_name_first_2</th>\n",
+       "      <th>distance</th>\n",
+       "      <th>walking_time</th>\n",
+       "      <th>monotonically_increasing_id</th>\n",
+       "    </tr>\n",
+       "  </thead>\n",
+       "  <tbody>\n",
+       "    <tr>\n",
+       "      <th>2256</th>\n",
+       "      <td>2938</td>\n",
+       "      <td>8590551</td>\n",
+       "      <td>503</td>\n",
+       "      <td>47.394665</td>\n",
+       "      <td>8.631157</td>\n",
+       "      <td>Dübendorf, Branzenäsch</td>\n",
+       "      <td>8590587</td>\n",
+       "      <td>414</td>\n",
+       "      <td>47.393053</td>\n",
+       "      <td>8.633367</td>\n",
+       "      <td>Dübendorf, Sonnenberg</td>\n",
+       "      <td>0.244501</td>\n",
+       "      <td>293</td>\n",
+       "      <td>618475290624</td>\n",
+       "    </tr>\n",
+       "    <tr>\n",
+       "      <th>2257</th>\n",
+       "      <td>2939</td>\n",
+       "      <td>8590551</td>\n",
+       "      <td>503</td>\n",
+       "      <td>47.394665</td>\n",
+       "      <td>8.631157</td>\n",
+       "      <td>Dübendorf, Branzenäsch</td>\n",
+       "      <td>8590555</td>\n",
+       "      <td>599</td>\n",
+       "      <td>47.394877</td>\n",
+       "      <td>8.628714</td>\n",
+       "      <td>Dübendorf, Claridenstrasse</td>\n",
+       "      <td>0.185439</td>\n",
+       "      <td>222</td>\n",
+       "      <td>618475290625</td>\n",
+       "    </tr>\n",
+       "    <tr>\n",
+       "      <th>2258</th>\n",
+       "      <td>2940</td>\n",
+       "      <td>8590551</td>\n",
+       "      <td>503</td>\n",
+       "      <td>47.394665</td>\n",
+       "      <td>8.631157</td>\n",
+       "      <td>Dübendorf, Branzenäsch</td>\n",
+       "      <td>8590581</td>\n",
+       "      <td>886</td>\n",
+       "      <td>47.391557</td>\n",
+       "      <td>8.634876</td>\n",
+       "      <td>Dübendorf, Raubbühl</td>\n",
+       "      <td>0.444715</td>\n",
+       "      <td>533</td>\n",
+       "      <td>618475290626</td>\n",
+       "    </tr>\n",
+       "    <tr>\n",
+       "      <th>2259</th>\n",
+       "      <td>2941</td>\n",
+       "      <td>8590551</td>\n",
+       "      <td>503</td>\n",
+       "      <td>47.394665</td>\n",
+       "      <td>8.631157</td>\n",
+       "      <td>Dübendorf, Branzenäsch</td>\n",
+       "      <td>8590550</td>\n",
+       "      <td>931</td>\n",
+       "      <td>47.397048</td>\n",
+       "      <td>8.625614</td>\n",
+       "      <td>Dübendorf, Bettlistrasse</td>\n",
+       "      <td>0.494279</td>\n",
+       "      <td>593</td>\n",
+       "      <td>618475290627</td>\n",
+       "    </tr>\n",
+       "    <tr>\n",
+       "      <th>2260</th>\n",
+       "      <td>2942</td>\n",
+       "      <td>8590551</td>\n",
+       "      <td>503</td>\n",
+       "      <td>47.394665</td>\n",
+       "      <td>8.631157</td>\n",
+       "      <td>Dübendorf, Branzenäsch</td>\n",
+       "      <td>8590590</td>\n",
+       "      <td>1226</td>\n",
+       "      <td>47.390535</td>\n",
+       "      <td>8.632469</td>\n",
+       "      <td>Dübendorf, Sunnhalde</td>\n",
+       "      <td>0.469644</td>\n",
+       "      <td>563</td>\n",
+       "      <td>618475290628</td>\n",
+       "    </tr>\n",
+       "    <tr>\n",
+       "      <th>2261</th>\n",
+       "      <td>2943</td>\n",
+       "      <td>8590551</td>\n",
+       "      <td>503</td>\n",
+       "      <td>47.394665</td>\n",
+       "      <td>8.631157</td>\n",
+       "      <td>Dübendorf, Branzenäsch</td>\n",
+       "      <td>8590562</td>\n",
+       "      <td>1244</td>\n",
+       "      <td>47.396240</td>\n",
+       "      <td>8.629935</td>\n",
+       "      <td>Dübendorf, Glärnischstrasse</td>\n",
+       "      <td>0.197806</td>\n",
+       "      <td>237</td>\n",
+       "      <td>618475290629</td>\n",
+       "    </tr>\n",
+       "    <tr>\n",
+       "      <th>2262</th>\n",
+       "      <td>2944</td>\n",
+       "      <td>8590551</td>\n",
+       "      <td>503</td>\n",
+       "      <td>47.394665</td>\n",
+       "      <td>8.631157</td>\n",
+       "      <td>Dübendorf, Branzenäsch</td>\n",
+       "      <td>8590549</td>\n",
+       "      <td>1392</td>\n",
+       "      <td>47.394817</td>\n",
+       "      <td>8.634580</td>\n",
+       "      <td>Dübendorf, Bauhof</td>\n",
+       "      <td>0.258181</td>\n",
+       "      <td>309</td>\n",
+       "      <td>618475290630</td>\n",
+       "    </tr>\n",
+       "  </tbody>\n",
+       "</table>\n",
+       "</div>"
+      ],
+      "text/plain": [
+       "      index  stop_id_general  stop_int  stop_lat_first  stop_lon_first  \\\n",
+       "2256   2938          8590551       503       47.394665        8.631157   \n",
+       "2257   2939          8590551       503       47.394665        8.631157   \n",
+       "2258   2940          8590551       503       47.394665        8.631157   \n",
+       "2259   2941          8590551       503       47.394665        8.631157   \n",
+       "2260   2942          8590551       503       47.394665        8.631157   \n",
+       "2261   2943          8590551       503       47.394665        8.631157   \n",
+       "2262   2944          8590551       503       47.394665        8.631157   \n",
+       "\n",
+       "             stop_name_first  stop_id_general_2  stop_int_2  stop_lat_first_2  \\\n",
+       "2256  Dübendorf, Branzenäsch            8590587         414         47.393053   \n",
+       "2257  Dübendorf, Branzenäsch            8590555         599         47.394877   \n",
+       "2258  Dübendorf, Branzenäsch            8590581         886         47.391557   \n",
+       "2259  Dübendorf, Branzenäsch            8590550         931         47.397048   \n",
+       "2260  Dübendorf, Branzenäsch            8590590        1226         47.390535   \n",
+       "2261  Dübendorf, Branzenäsch            8590562        1244         47.396240   \n",
+       "2262  Dübendorf, Branzenäsch            8590549        1392         47.394817   \n",
+       "\n",
+       "      stop_lon_first_2            stop_name_first_2  distance  walking_time  \\\n",
+       "2256          8.633367        Dübendorf, Sonnenberg  0.244501           293   \n",
+       "2257          8.628714   Dübendorf, Claridenstrasse  0.185439           222   \n",
+       "2258          8.634876          Dübendorf, Raubbühl  0.444715           533   \n",
+       "2259          8.625614     Dübendorf, Bettlistrasse  0.494279           593   \n",
+       "2260          8.632469         Dübendorf, Sunnhalde  0.469644           563   \n",
+       "2261          8.629935  Dübendorf, Glärnischstrasse  0.197806           237   \n",
+       "2262          8.634580            Dübendorf, Bauhof  0.258181           309   \n",
+       "\n",
+       "      monotonically_increasing_id  \n",
+       "2256                 618475290624  \n",
+       "2257                 618475290625  \n",
+       "2258                 618475290626  \n",
+       "2259                 618475290627  \n",
+       "2260                 618475290628  \n",
+       "2261                 618475290629  \n",
+       "2262                 618475290630  "
+      ]
+     },
+     "execution_count": 74,
+     "metadata": {},
+     "output_type": "execute_result"
+    }
+   ],
+   "source": [
+    "# footpaths from Dübendorf, Branzenäsch\n",
+    "transfers[transfers['stop_id_general']== 8590551]"
+   ]
+  },
+  {
+   "cell_type": "markdown",
+   "metadata": {},
+   "source": [
+    "No sign of Uetliberg here."
+   ]
+  },
+  {
+   "cell_type": "code",
+   "execution_count": 75,
+   "metadata": {},
+   "outputs": [
+    {
+     "data": {
+      "text/html": [
+       "<div>\n",
+       "<style scoped>\n",
+       "    .dataframe tbody tr th:only-of-type {\n",
+       "        vertical-align: middle;\n",
+       "    }\n",
+       "\n",
+       "    .dataframe tbody tr th {\n",
+       "        vertical-align: top;\n",
+       "    }\n",
+       "\n",
+       "    .dataframe thead th {\n",
+       "        text-align: right;\n",
+       "    }\n",
+       "</style>\n",
+       "<table border=\"1\" class=\"dataframe\">\n",
+       "  <thead>\n",
+       "    <tr style=\"text-align: right;\">\n",
+       "      <th></th>\n",
+       "      <th>index</th>\n",
+       "      <th>stop_id_general</th>\n",
+       "      <th>stop_int</th>\n",
+       "      <th>stop_lat_first</th>\n",
+       "      <th>stop_lon_first</th>\n",
+       "      <th>stop_name_first</th>\n",
+       "      <th>stop_id_general_2</th>\n",
+       "      <th>stop_int_2</th>\n",
+       "      <th>stop_lat_first_2</th>\n",
+       "      <th>stop_lon_first_2</th>\n",
+       "      <th>stop_name_first_2</th>\n",
+       "      <th>distance</th>\n",
+       "      <th>walking_time</th>\n",
+       "      <th>monotonically_increasing_id</th>\n",
+       "    </tr>\n",
+       "  </thead>\n",
+       "  <tbody>\n",
+       "  </tbody>\n",
+       "</table>\n",
+       "</div>"
+      ],
+      "text/plain": [
+       "Empty DataFrame\n",
+       "Columns: [index, stop_id_general, stop_int, stop_lat_first, stop_lon_first, stop_name_first, stop_id_general_2, stop_int_2, stop_lat_first_2, stop_lon_first_2, stop_name_first_2, distance, walking_time, monotonically_increasing_id]\n",
+       "Index: []"
+      ]
+     },
+     "execution_count": 75,
+     "metadata": {},
+     "output_type": "execute_result"
+    }
+   ],
+   "source": [
+    "# transfers from Uetliberg (stop 8503057)\n",
+    "transfers[transfers['stop_id_general']== 8503057]"
+   ]
+  },
+  {
+   "cell_type": "markdown",
+   "metadata": {},
+   "source": [
+    "Again, utliberg has no footpaths, like Dallikon Industrie in the previous bug."
+   ]
+  },
+  {
+   "cell_type": "code",
+   "execution_count": 79,
+   "metadata": {},
+   "outputs": [
+    {
+     "data": {
+      "text/plain": [
+       "array([[5599, 2253.0],\n",
+       "       [5603, 2256.0],\n",
+       "       [5606, 2263.0]], dtype=object)"
+      ]
+     },
+     "execution_count": 79,
+     "metadata": {},
+     "output_type": "execute_result"
+    }
+   ],
+   "source": [
+    "# footpaths from Dübendorf, Branzenäsch\n",
+    "stop_int = 503\n",
+    "stops[stop_int-1:stop_int+2]"
+   ]
+  },
+  {
+   "cell_type": "code",
+   "execution_count": 80,
+   "metadata": {},
+   "outputs": [
+    {
+     "data": {
+      "text/plain": [
+       "array([[ 414,  293],\n",
+       "       [ 599,  222],\n",
+       "       [ 886,  533],\n",
+       "       [ 931,  593],\n",
+       "       [1226,  563],\n",
+       "       [1244,  237],\n",
+       "       [1392,  309]])"
+      ]
+     },
+     "execution_count": 80,
+     "metadata": {},
+     "output_type": "execute_result"
+    }
+   ],
+   "source": [
+    "transfer_array[int(stops[stop_int][1]):int(stops[stop_int+1][1])]"
+   ]
+  },
+  {
+   "cell_type": "code",
+   "execution_count": 51,
+   "metadata": {},
+   "outputs": [
+    {
+     "data": {
+      "text/plain": [
+       "array([[5599, 2253.0],\n",
+       "       [5603, 2256.0]], dtype=object)"
+      ]
+     },
+     "execution_count": 51,
+     "metadata": {},
+     "output_type": "execute_result"
+    }
+   ],
+   "source": [
+    "stops[stop_int-1:stop_int+1]"
+   ]
+  },
+  {
+   "cell_type": "code",
+   "execution_count": null,
+   "metadata": {},
+   "outputs": [],
+   "source": []
+  }
+ ],
+ "metadata": {
+  "kernelspec": {
+   "display_name": "Python 3",
+   "language": "python",
+   "name": "python3"
+  },
+  "language_info": {
+   "codemirror_mode": {
+    "name": "ipython",
+    "version": 3
+   },
+   "file_extension": ".py",
+   "mimetype": "text/x-python",
+   "name": "python",
+   "nbconvert_exporter": "python",
+   "pygments_lexer": "ipython3",
+   "version": "3.7.6"
+  }
+ },
+ "nbformat": 4,
+ "nbformat_minor": 4
+}