Free sources for georeferenced topographic maps you can load straight into GeoMapViewer — as GeoTIFF or GeoPDF, with live GPS on top.
Larger scale = more detail over a smaller area. A quick guide for choosing a sheet:
The National Map & topoView
United States
The USGS publishes the current US Topo series (2009–present) and the scanned Historical Topographic Map Collection (1884–2006). Both follow the classic 7.5-minute quadrangle layout at 1:24,000 — the gold standard for US backcountry detail. topoView is the easiest browser for finding and downloading sheets; The National Map Downloader covers the current series.
topoView
The National Map Downloader
National coverage
Australia · National
The national mapping agency offers free 1:50,000, 1:100,000, 1:250,000 and 1:1,000,000 sheets through interactive index dashboards — pick a tile, then download. The newer AUSTopo 1:250,000 series is rolling out as fresh GeoPDFs. Note that Geoscience Australia does not hold 1:25,000 maps — for those, go to the relevant state or territory agency (see NSW below).
Topographic maps (index dashboards)
The finest-detail Australian state series
Australia · New South Wales
DCS Spatial Services publishes the NSW Topographic Map series as georeferenced PDFs you download yourself from the Spatial Collaboration Portal. Scale follows the terrain: roughly 1:25,000 across the populated east and coast, 1:50,000 through the centre, and 1:100,000 in the far west. Released under Creative Commons (CC BY 4.0), so free to use and print.
NSW Topographic Maps
Topo50 series
New Zealand
Land Information New Zealand's Topo50 is the official 1:50,000 series covering the mainland, Chatham and offshore islands (some islands at 1:25,000). Georeferenced raster images are published at 300 DPI under CC BY 4.0. Use the Topo50 Map Chooser to grab a single sheet, or the LINZ Data Service for georeferenced downloads and bulk access.
Topo50 Map Chooser
LINZ Data Service (georeferenced)
A two-part answer
United Kingdom
OS is the UK's national mapping agency, but unlike the others its current walking maps are not free. The Explorer (1:25,000) and Landranger (1:50,000) Colour Raster products are sold as GeoTIFF through the OS Data Hub or licensed partners. What is free on the OS Data Hub is OS OpenData — but only at smaller scales (1:250,000 Colour Raster, VectorMap District, OpenMap Local). Good as backdrops; not hiking detail.
OS Data Hub — OpenData downloads
United Kingdom · Free & georeferenced
For free, hiking-scale, properly georeferenced UK mapping, the NLS is the answer. It serves out-of-copyright OS maps for the whole of Great Britain as georeferenced GeoTIFF (British National Grid, EPSG:27700) under CC-BY — including the One-Inch (1:63,360, the Landranger's ancestor) and Six-Inch (1:10,560) series. Historic rather than current, but excellent for exploring and superb terrain detail.
NLS Georeferenced Maps viewer
The workflow is the same wherever the file comes from:
GeoMapViewer reads georeferenced .tif / .tiff and georeferenced .pdf. A plain scan without coordinates won't position on the map.
Full-resolution quads can run to tens of megabytes. Download over Wi-Fi before you lose signal, then they work fully offline.
Each source uses its own datum — UTM, NZTM2000, British National Grid (EPSG:27700) and others. GeoMapViewer reads the system embedded in the file.
A road or track on a map doesn't guarantee public access. Check with the relevant land manager before crossing private or restricted land.
Links to USGS, Geoscience Australia, NSW Spatial Services, LINZ, Ordnance Survey & the National Library of Scotland. Availability, formats and licences are set by each agency and may change.