Hiker Discovery Walking Guides
Digital Maps
Mobile Atlas Tiles

This is a standard way of storing and delivering maps to mobile devices. The standard is similar to that used for Google Maps.

The maps are based on a Spherical Mercator Projection. Each map tile is square and 256x256 pixels in size. At zoom level 0, one tile covers the whole Earth (up to about 84 degrees latitude), at zoom level 1 there are four tiles each covering half a hemisphere, and so on up to about zoom level 17 which is roughly equivalent to a 1:25000 map. So in an atlas, each tile has three coordinates X,Y and Z. Z is the zoom level and X and Y are the tile positions counting east and south from the origin point north of the Bering Strait. The tile coordinate system means no separate calibration file is needed.

But the 'standard' is implemented in different ways. Some systems use tiles as JPG images, some as PNG. Different systems address the coordinates in a different sequence : X/Y/Z.png or Z/X/Y.png, for example. Some systems pack the tiles either with a 'zip' or 'tar' program or use a SQLite Database; some add suffixes such as '.tile' or 'andnav' to the tile name; some systems allow tiles to be prepared offline and some expect to download them as needed.

Because they are based on a Spherical Mercator projection these tiles cannot just be 'cut' from a traditional map. The map has to be reprojected - essentially to stretch the map by progressive amounts the further it is from the equator - and padded to make it a whole number of tiles.

There is a program MAPC2MAPC (Windows only) which will take these Discovery Walking Guides maps and make them into some of the formats of Mobile Atlas that can be downloaded to the device from a PC. Download the Discovery Map, unpack the zip archive and open the .MAP in MAPC2MAPC then use File>Write Mobile Atlas. The process will take several minutes to reproject the map. At present these are :

  Maverick : Z/X/Y.png.tile   sample
  Andnav    : Z/X/Y.png.andnav   sample
  OSMTracker : Z/X/Y.png (also Palm Maptool)   sample
  Back Country Navigator : Z/X/Y.png.bcnav   sample

Click on 'sample' above to download a test file in this format.