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