OpenStreetMap
When I looked at OSM for trip planning in Namibia, I simply assumed that the empty spaces on the slippy map meant that the data just wasn't there.
Now, as I try to upload some data, it turns out that it's actually very complete: pretty much all major roads in the country are there!
It's just that they are marked as "highway:tertiary" and "surface:unpaved". Except for a handful of main arteries, all roads in that country are, indeed, unpaved gravel roads, but since you can often drive over 100km/h on them (that's actually the official speed limit, even if it's definitely not always a smart thing to do) and since they're the only way in which cities (by Namibian standards) are interconnected, it's hardly fair to call them tertiary roads...
A nice example is here: http://openstreetmap.com/?lat=-24.426&lon=16.1727&zoom=12&layers=B000FTF
No matter now deep you zoom in, you'll never be able the discover that you're actually looking at the intersection of roads D854 and D850... The labels are never rendered.
In all honesty, those roads don't even show up on Google Maps, but at least it shows the C roads (highest standard gravel roads) in all its glory and some cities.
Also, so other D-roads are tagged as secondary and will show up if you zoom in very closely.
It's probably pretty hard to implement, but a possible solution would be to render detail density adaptive: when there's little or no roads in the area, label roads and mark cities even if they normally wouldn't show up in densly populated area.
As similar example is here: http://openstreetmap.com/?lat=-23.8931&lon=16.0022&zoom=13&layers=B000FTF
Solitaire is a hamlet (as tagged on the map), probably of no more than 100 inhabitants, if that much. But when it's the only place with a shop and gas in an area of, say, a hundred kilometers, it probably makes sense to make it a very prominent hamlet indeed, as is the case on Google Maps:
http://maps.google.com/?ie=UTF8&ll=-24.557116,15.869751&spn=2.792765,4.839478&z=8
(Yahoo Maps is far worse then OSM, BTW!)
Discussion
Comment from ColinMarquardt on 25 May 2009 at 20:41
A small improvement would be to correctly tag the "D854", "D850" etc. as ref, not as name so that they are displayed with a shield. And I agree they should be rated higher than tertiary (from your report and that of a friend).
Comment from wallclimber21 on 26 May 2009 at 01:10
I just checked it out: the road has been tagged both name:D850 and ref:D850. That should be sufficient, right?
I assume the combination of tertiary and unpaved is what's doing it in...
Comment from daveemtb on 26 May 2009 at 06:15
I agree that an adaptive renderer is needed. The maps of most of Africa are pretty useless at the moment, and this is one of the areas that OSM can be of most use.
Comment from IgnoredAmbience on 26 May 2009 at 06:42
Label rendering is an outstanding issue with mapnik, it tends to only render a name once on a way, meaning that on very long ones, they may get lost in the middle somewhere. It should however render shields more frequently, in fact one is visible on the D854 3 zooms in from your first link.
The unpaved tag should have no impact upon its rendering, since I don't think its yet used at all.
In this case, since these roads are the best the country has, I'd be very tempted to promote them to primary / secondary roads as appropriate. We already do have allowances for the usual highway types to be defined on a per-country basis - http://wiki.openstreetmap.org/wiki/Key:highway#International_equivalence
Comment from alv on 26 May 2009 at 06:57
The key surface is not even looked at in the rendering rules, AFAIK.
Comment from Peter Dörrie on 26 May 2009 at 07:03
Yes, countries like Kenya should get an adapted (or at least thought over) definition of highway types. But still, one should take care that things like motorway and trunk are not applied to gravel roads, just because they are the best highways.
Comment from ColinMarquardt on 26 May 2009 at 19:14
Oh, I incorrectly assumed ref was not set at all, I just saw the name written along the road. I thought steve8 had fixed the frequency of the shield rendering, but maybe not for all highway types and/or all zooms.