How an Offline Map Knows Which Paris You Mean
Search in a map app looks like one operation: type a place, get a result. In an offline map it is two decisions. First, understand what the words mean. Then decide which local map files are worth searching.
GLMap keeps streets, addresses, and places in detailed regional maps. Alongside them is a compact world map containing countries, regions, and important cities. One C++ search engine uses these sources on iOS, Android, and in our online search service.
The map center normally tells the engine where to start. If you are in Warsaw and type cafe, that
is exactly what you want. But suppose you are planning a trip and type
Eiffel Tower Paris France. The map is still centered on Warsaw; the words clearly point to Paris.
Search only around Warsaw and the Eiffel Tower never appears. Search every regional map and even a simple autocomplete request may open files across the planet. The rule we arrived at is: the map center is a bias; geography written by the user is intent.
Over the past months we rebuilt GLMap search around that rule. It can now route the Eiffel Tower
query to France, find Wrocław from the keyboard-friendly spelling Wroclaw, keep Paris Optique
in Warsaw, and find a small village missing from the world map — all while the phone is in airplane
mode.