Custom map images can be added to the app using the following format.

Projection: NZTM2000

Tile size: 1024 by 1024 pixels

File format: jpeg

Filename format: mzzxxxxyyyy.jpg where zz is the scale index, xxxx is the easting index from the reference easting, and yyyy is the northing index from the reference northing. Easting and northing indexes are zero based and relative to the western and northern most corner (top left) of the image.

Reference easting: 1560000 (North), 1080000 (South)

Reference northing: 6200000 (North), 5550000 (South)

Scale: 0.47244 pixels per meter for zz=10, 0.23622 pixels per meter for zz=09, 0.11811 pixels per meter for zz=08, 0.05905 pixels per meter for zz=07, etc

To use the custom images, save them to a directory on your phone and then select this directory from the custom map selector on the settings page in the app.

Example image sets that you can try include satellite images for the north and south islands from the LINZ Basemaps series, at a scale of 0.47244 pixels per meter. These are zip files that will need to be unzipped before copying to your phone. Note that the file size and number of files is quite large and some phones may take a while to manage them all.