AlpineQuest & OfflineMaps

Here we see the typical Chicago subway station sign. On it we see the grid location. Wouldn't it be great if the app could also do this as a secondary coordinate display.

Okay, the user has just arrived in Chicago and put center of the screen at the corner of State and Madison and tells the app the grid shall be 800 numbers per mile both east and west and north and south. Presto!

Now some cities addresses don't exactly go north and south, so the user could put in some degrees tilt specification, too!

Anyway the app should display 1200 N 1600 W when we are at that spot.

Sure, you might say Chicago has some irregularities, especially in the first mile southbound, but let's just do the simplest version for starters. Also perhaps the app could have pre-defined modes for your common grid-like cities: Edmonton, Los Angeles, you name it.

If one has grown up in Europe, one cannot imagine a use for all this. But for one who has grown up in North America, this concept is super duper!

Okay now we're crossing the border of Chicago to Evanston and now we need to switch to the Evanston grid mode. Well of course that's another tricky issue. Or maybe we still want to know Chicago grid value even though we are now in some suburb. Also note some suburbs do use the Chicago grid.

Anyway, some people might want to see the metropolitan area grid, the local suburb grid, and even longitude and latitude, all displayed at the same time.

If I correctly understand those coordinates only apply to Chicago?
Can't you deduce them from the lat/long coordinates? Cause adding a coordinate system for just a city is a bit too restrictive...