Question

I am working on a new project and whole day thinking & looking for the best way, how to save users’ location to database.

I need to save their city, country. Here is a bit problem, because for example for Europeans this means city=Berlin, country=Germany.
But for US users it’s like city=Los Angeles, country=California (state=USA).

So this is the problem with which I ma facing whole today.

My goal in this app is to find all users in the city according to their location. And also find the people, which are in their area of let’s say 15 km/miles.

I plan to implement the app in RoR, PostgreSQL, the app will run probably on Heroku.

What is the best way to solve this “problem”? Could you give me please some advices, tips, whatever?

Thank you

Answer 1

You can use the geokit and geokit-rails gems to achieve that. See here for documentation: https://github.com/imajes/geokit-rails

Basically, it works like this: you save address data of your users and that address is looked up and mapped to a point in space (lat/lng) using a geocoding service (e.g. Google Maps or Yahoo Placefinder). These points can then be used to calculate distances etc.

An example:

class User < ActiveRecord::Base
  # has the following db fields:
  # - city
  # - state
  # - country
  # - latitude
  # - longitude

  acts_as_mappable :default_units       => :miles, 
                   :default_formula     => :sphere, 
                   :lat_column_name     => :latitude,
                   :lng_column_name     => :longitude,
                   :auto_geocode        => {:field => :full_address}

  def full_address
    [city, state, country].reject(&:blank).join(', ')
  end
end

Then you can do the following:

# find all users in a city (this has nothing to do with geokit but is just a normal db lookup)
User.where(:city => 'New York')

# find all users that are within X miles of a place
User.find_within(300, 'Denver')

and much more, just see the documentation…

This example shows you how to use the geokit gem. This gem does no longer seem to be under active development. So maybe it would be worthwile to check out geocoder: https://github.com/alexreisner/geocoder