The original coordinates that define the objects making up a map are stored in long integer format, in their genuine units coded in integer "internal" units, after some linear transformations according to the situation:
Long\Lat "unbounded" is a unique case: the coordinates are registered in millionths of a degree and the range of internal units are set to correspond to +-90 millions for Latitude, and to +-360 millions for Longitude
In all the other situations, (Long\Lat bounded, projected bounded\unbounded, and Non-Earth explicitly bounded), the minimum x bound is set to -1 billion in internal units and the maximum to +1 billion of these units; and the same for minimum Y and maximum Y. The genuine coordinates are converted by linear transformation using these parameters into internal units. The x and Y transformations are independent, being based on the X and Y ranges that can be different.
ex (external coordinate)exmax, exmin (Max, Min of external coordinate, the bounds)ix (internal coordinate) = int [( ex - exmin) / (exmax - exmin) * 2
billion] - 1 billionThe parameters of the linear transformations (exmax, exmin) are kept in double precision (15 significant digits) as are the projection parameters; the internal coordinate as a long integer.