Perfectly rectangular buildings (in OSM) shown distorted (in GPSr)

There are plenty of perfectly rectangular buildings on maps in OSM. After processing them with Splitter and Mkgmap, and viewing them on the GPSr, these buildings don’t show up properly rectangular anymore, but distorted: askew, triangular, lopsided, etc. What causes this, and what do I need to do to prevent it.

I notice the effect with my own creations, and also with Freizeikarte-osm pre-made IMG files.

Regards, Wim van Dorst

Garmin map format uses integer values to describe position. All objects on a map are drown on a grid with a distance between points about 2m. This feature distorts small objects like buildings.