The defaults remains the same: Bay area at zoom 15.
The key, if not supplied, is taken from the environment.
```
Allowed options:
-s [ --style ] URL Map stylesheet
--north degrees (=37.200000000000003) North latitude
--west degrees (=-122.8) West longitude
--south degrees (=38.100000000000001) South latitude
--east degrees (=-121.7) East longitude
--minZoom number (=0) Min zoom level
--maxZoom number (=15) Max zoom level
--pixelRatio number (=1) Pixel ratio
-t [ --token ] key Mapbox access token
-o [ --output ] file (=offline.db) Output database file name
```
* Under the hood, SQLite creates surrogate keys (ROWID) anyway. We may as well take advantage of this and use the surrogates for foreign keys as well, since they are simpler and more efficient than compound foreign keys.
* Create indexes for efficient eviction queries
