I’ve been looking at the other islands in the Commonwealth of Northern Marianas Islands, and it looks like all the TIGER data is in a sad state. I think I’ll start with Rota and begin editing the roads by hand. There aren’t a lot of them, only 377 TIGER roads, and Rota is a lovely island that deserves the attention.

I think the roads are less distorted in Rota than in Saipan because it’s closer to Guam, which was used as a survey base for many of the older maps.

I don’t have good GPS data for Rota, but I’ll ask my friends up there to see what they can do for me. The satellite imagery is also pretty well registered, from what I’ve seen. If all else fails, it’s a good excuse for a vacation to Rota for a few days.

I’ve noticed that while the data for Guam is generally pretty good, the data for Saipan is in a pretty sad state. In particular, the streets are distorted, and up to 60 meter off from their true location. You can see this by loading the streets on a Bing or other satellite image. This is starting to create problems for folks using GPS and other tools that use OpenStreetMap as a base source.

Most of this appears to be due to bad TIGER data during the 2008 import. Back in the bad old days, Saipan and the rest of the CNMI used a variety of old datums and projections, some of which weren’t clearly documented. The TIGER data was on one of these, as was a lot of our old data from USGS, and the roads and related data are offset and distorted as a result. Even Google Earth uses bad old data.

My goal over the next six months is to replace all the distorted road data with TIGER 2012 data, or with equivalent data sourced directly from the government of the CNMI (i.e. Saipan). I’m frequently on Saipan and have worked with their data and analysts, so am confident that I can make this work.

Most of the TIGER data for Saipan is unreviewed and unedited, so doing a batch replace will have limited impact on existing users’ work. A similar project was done for [parts of Alaska by pnorman] (osm.wiki/Alaska/TIGER_Counties‎).

Things to do: 1. Update shoreline with NOAA data 2. Update shoreline with 2013 imagery to reflect ongoing erosion 3. Locate appropriate data 4. Figure out the scope of the problem (e.g. only roads, all TIGER linework, GNIS?) 5. Make sure folks in the area/community are on-board. 6. Prioritize fixes (probably start w/ roads, as that’s most annoying to me) 7. Start implementing fixes by priority 8. On-the-ground GPS work to check fixes 9. Invite other folks to review