Natmap topo 1:250,000 are available free. See access details below. You can view these just with a PDF viewer or add them to the Avenza Maps app when you select d/l as georeferenced PDFs. This app provides GPS functions. For outback these are IMO the best maps available - by that I mean have the most geographic information. There are two limitations: they can be fairly old and the scale is too small for fine navigation. That second point means they're not my first choice for mountain country where there are numerous tracks that may not be signposted. Download: advice from the publisher To access each map, using our topographic map index (see http://www.ga.gov.au/metadata-gateway/metadata/record/75410/), identify the name of the map that you would like, then type the map name into the ‘Data and Publications Search’ (http://www.ga.gov.au/search/index.html#/) to locate and download each map. (Note: the index covers 100K topos as well. Take care to compare them against the 250s; many users found them inadequate). By using our Interactive Maps (http://www.ga.gov.au/interactive-maps/#/theme/national-location-information/map/australiantopography), to customise your area of interest and then save as a pdf. (Note: this isn't working for me at the moment and there's a query in with GA). Use with Avenza Maps app If you have more money than time you may prefer to go down the paid route. You can d/l these maps within Avenza. Some you'll have to buy. Or the no-cost option is to d/l them as georeferenced PDFs and run them in an old version of free Avenza which doesn't have the limit of 3 of your own sourced maps. That's around v1.7.3 which you'll have to load via the side door, ie. outside of the Google or Apple stores. (Search for Avenza 1.7.3 APK. Beware hacked versions; the installation should not ask you to do anything). Alternatively, in the free version of the app from Google Play or the App Store buy the USD30 per year upgrade which allows unlimited own-source maps.