With the purpose of doing a real time satellite positioning on computerised maps using GPS system we have done some map processing before having put them in use. It was found out that better results are obtained when the maps are scanned with high informational rate which is later reduced using image processing techniques, compared to map scanning in the mode they are visualised. Because of the large amount of involved data the need of a compression that allows very fast decompression is obvious. Therefore the RLE encoding on binary images and the JPEG algorithm on grey level images were implemented. The precision of the GPS positioning was increased using data filtering and smoothing.