MyTopo used to be the go-to source for web-compatible topo maps, but Trimble bought them, and after 9 months of business as usual, decided it was time to take their ball and go home. You can still include their map tiles in a web app if you (1) pay them a bundle of money or (2) can live with watermarks that take up half the image. I'm not sure if using them in a smartphone app is even an option. It's a shame because MyTopo's map layer had a couple things going for it:
- Seamlessly integrated Forest Service maps. They made some bold claims about updating maps to reflect new USFS roads and trails, but in reality it seems like they took the Primary Base Series raster maps and added in vegetation shading, which is still no easy task.
- Canada and Alaska coverage.
- Normalized colors across scans. Each quad used exactly the same color for white, green, brown, etc.
ESRI makes a number of maps available via WMS and a web tile scheme, including a topo layer based on scanned USGS maps. All their licensing information seems directed at ArcGIS end-users and not websites, but it says nothing to indicate that you can't pull it into a web map. These maps cover Alaska but not Canada; unfortunately the image quality is lower than I'd like to see. They only go to zoom 15 v. CalTopo's 16, and even then you can see serious artifacting that suggests the images were over-compressed.
The National Map is run by the USGS and offers up a mishmash of layers via a mishmash of access schemes. Much like Terraserver, they have the older low-res DRG scans available through WMS. Although the scans leave a lot to be desired, this service seems like a good Terraserver stand-in for now.
And of course there's my favorite high-res map layer, CalTopo. The USGS has finished high-res scans for all of the continental US except MA, so it's time to take another pass and fix some of the coverage gaps I ran into in January. If you'd like to include any the CalTopo map layers in your web site / iPhone app / whatever, send me an email and we can work out the details.