Fred asked: "My other question is about the available maps. The article mentions several, which appear to be raster maps. How well do these handle zooming? If you load one to show enough detail for small roads, does it blur into uselessness when you zoom out to view a county, or does it drop detail like the vector maps that are made for purpose-made GPSRs?"
In the article I mentioned four map types, and the zooming depends on the map type.
For OpenStreetMaps and OpenCycleMaps, go to OpenCycleMap.org or OpenStreetMap.org on your desktop machine to see how zooming is handled; it looks the same on the iPhone, Android, or iPad.
Here is the Marin Headlands at zoom 15, you can zoom in and out from there:
http://www.openstreetmap.org/?lat=37.8328&lon=-122.48284&zoom=15&layers=CThese are vector maps. OpenCycleMap supports ~17 zoom levels. Both Gaia GPS and GPS Kit are great apps if you're using OpenCycleMap. You can specify which zoom levels you want to download for offline use. If you care about altitude lines (i.e. topo map) then you use the CycleMap view; if not, then you use the StreetMap (aka Mapnik) view.
Apps that display USGS topos generally only have one or two zoom levels, 1:24K (and sometimes 1:100K), but that is all you need for hiking and that map sources is generally not relevant for road biking. These are raster maps. Topo Maps is an exceptional app for USGS and NRCan maps.
For Satellite images, using Trail Maps by National Geographic you get bing hybrid maps. It only includes one zoom level of Sat image and the resolution is good enough to easily see buildings, but making out individual cars is marginal. When you zoom in and out it just magnifies the image, but does not replace it with a different source image.
For road maps in the US, I use ForeverMap by Skobbler, and zooming is just fine, with clarity at all zoom levels and more details shown at each successive zoom level. These are vector maps. This app does rudimentary routing, nothing fancy. When you download a map (you download one state at a time), it includes wiki entries, which is a nice feature. I didn't study all the other options for road maps, so I don't know that this is the best app, but it's plenty good enough, and cheap too.
For cycle route maps, Maplets has many good cycle route maps. But those maps have just one zoom level; think of it as an electronic version of a pdf printed map, except that your location is shown on the map. It's a fantastic little app to use in conjunction with other apps, it has no bells or whistles, but it gives you the ability to find maps you didn't know existed, and when the maps are drawn to scale you can see your position on the map. You can see which maps are available by searching for a location, or just search for the word cycle to get a sense for their current inventory:
http://www.mobilemaplets.com/placesIf you know of a map (pdf or gif or whatever format) that they don't have, just request it and they will do their best to add it.
Unlike Boglesan, I wouldn't recommend trying to find good apps by browsing the iTunes store. I have now evaluated 75 different mapping/gps apps, and have found fewer than a dozen that I think are worth using. Some of them are pure crap. Sometimes you can tell from the description in the store if the app will be useful, but not consistently. I do agree that the iPad/iPhone user forums would be good places to get recommendations and opinions, and that the Apple Apps store is anemic if you're trying to find something.
If you're looking for iPad/iPhone apps, you can start with the list I've built, and go from there. Please let me know of good mapping/gps apps that I've missed.
http://dl.dropbox.com/u/15393086/BPL/iPhoneGPSapps.htm
