Bad data at Bon Tempe Lake

December 29, 2009 at 12:00 PM in: maps

Got the dynamic range right on the shaded relief. (Click image for 1024x1024 version):

Alpine Lake and Bon Tempe Lake

Alpine Lake and Bon Tempe Lake (CC-by-SA license)

I've spent several days trying to figure out why the roads in the MRLC land cover data don't line up with the OpenStreetMap roads. The creeks (from NHD), elevation (from 10m NED), and roads all seem to line up in a way that matches aerial photographs. I double checked all projections, installed the latest versions of everything, lots of web research, no clue what's going on.  The roads seen in the landcover data are the right shape, they're just off in position. But they're off in position by a variable amount.

I finally noticed that the landcover doesn't even agree with itself! There are places where the landcover data indicates a road crossing open water and there is obviously no bridge. The dam on Bon Tempe lake shows that the vegetation and water are correctly aligned with OpenStreetMap, but the pink line for the road crossing the dam doesn't line up with the other landcover pixels.

Is this a known problem with MRLC?

Mt Tam Chiaroscuro

December 14, 2009 at 12:00 PM in: maps
North flank of Mt Tamalpais

North flank of Mt Tamalpais

I've been playing with making topo maps using elevation and land cover data. Enough is in place now that some of the bugs look interesting. My initial take on light and shadow turned out to be a bit aggressive.

At full size this image becomes very abstract and reminds me of camouflage. The stripes from the shaded relief look like some animal patterns, and the blockiness of the land cover data looks like MARPAT.

As a thumbnail it's more obvious what's going on:

North flank thumbnail