This map shows followers of the @GeoHipster account (representing GeoHipster on Twitter) whose Twitter profiles have the “location” attribute set (see below for some caveats). The location is geocoded using the Geonames API and a minor random component of usually a few hundred meters included.
Format-wise, either a geo-codable place name or lat-lon coordinates in WGS1984, separated by either a comma, a semi-colon, a slash or a vertical bar (this one: |) (e.g: “47.51 / 8.54”), are accepted input data.
Followers who have not filled in their location field are not displayed on the map. Similarly, followers whose account is private are not displayed on the map, since the bot cannot query their user information. Finally, giving several locations in one's Twitter profile affects the location in the map unpredictably or might prevent geocoding completely.
If you have filled in your location field but are not displayed on the map or in an unexpected place, the location is not properly geocodable by GeoNames. You can test the suitability of your location field's contents here using the search function (although there is some evidence that there can be differences between the search function and the API).
(For aficionados and aficionadas: geocoding is done using Python to access the GeoNames API and build a CSV file with all relevant information. Said file is then parsed and displayed using Leaflet and some plugins.)