You can add custom maps by editing the maps.json configuration file or tapping the Set map collection source button and setting a custom configuration URL. Save a georeferenced map image as jpg or png with a world file and use gdalinfo to obtain the image extent (coorner coordinates) and coordinate system. Use epsg.io to get the Proj4js projection definition.

Note: map image files should be as small as possible (<2MB) to improve performance since the entire image is loaded.

Tap on one of the available maps to save it to your device for offline use. Saved maps can be reordered by tapping the sort button in the navbar. Individual maps can be removed from device storage by long pressing on the list item and tapping Remove map from device. You can clear all maps from storage by tapping the Remove saved maps button above.

Tap on a saved map to open it. You can zoom in and out and pan around using pinch and swipe gestures. If you are located within the map bounds and have allowed access to your GPS, your location will be identified as a blue dot on the map. If you have internet access, you can toggle an online basemap below your overlay map by tapping on the more_vert button in the navbar. The overlay map opacity can be adjusted with the slider.

The active map and view settings are saved for the session but will be cleared out when the app or browser is closed.