Finding the closest station

For this to work, you’re going to need to run the longitude and latitude of all the stations through the haversine function. The trick will be finding the smallest distance to your current longitude and latitude, and saving this as a variable.

  • Start by defining a new function, and setting a variable within it for the smallest distance. The longest possible distance between two points on the Earth’s surface is 20036km, so this would be a good place to start the variable:

    def find_closest():
    smallest = 20036

  • Now you can use a for loop to iterate through all the stations. Let’s start by printing the data for each:

    for station in all_stations:
    print(station)

  • Run your program and type the following into the shell to get the list of stations:

    find_closest()

idle list stations

You should see a large list of dictionaries, with each dictionary looking something like this:

{'weather_stn_name': 'ACRG_ROOF', 'weather_stn_lat': 52.197834, 'weather_stn_id': 1648902, 'weather_stn_long': 0.125366}

The data we’re interested in is the 'weather_stn_lat' and 'weather_stn_long'. These are the values we want to use in the haversine function.

  • Go back to your program; you can now get those values in the find_closest function. Remove the print(station) line and then add the following:

    station_lon = station['weather_stn_long']
station_lat = station['weather_stn_lat']

  • Now that you have all the data, it can be run through the haversine function to find the station’s distance to you:

    distance = haversine(my_lon, my_lat, station_lon, station_lat)
print(distance)

  • Run the code again and type find_closest() in the shell again.

That’s a long list of distances.

  • Next, you need to find the smallest one and then save that station’s ID. If the distance is smaller than the smallest variable it can be saved, and then next time around the loop it can be checked again.

    if distance < smallest:
        smallest = distance
        closest_station = station['weather_stn_id']
return closest_station

Your find_closest function should now look like this:

def find_closest():
    smallest = 20036
    for station in all_stations:
        station_lon = station['weather_stn_long']
        station_lat = station['weather_stn_lat']
        distance = haversine(my_lon, my_lat, station_lon, station_lat)
        if distance < smallest:
            smallest = distance
            closest_station = station['weather_stn_id']
    return closest_station

Be really careful with the indents otherwise the function wont work properly.

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