Bruce: The new proposal of course requires double precision. I agree that conversion between geographic and mapping coordinates generally is not impractical. I think arc interpolation is not as issue, as GLIMS points will rarely be spaced by more than a few km, the fractional error is roughly linear with spacing, and at 10 km is < 1.E-5 . My sole remaining concern is tracking of absolute location uncertainty and how to update all points associated with an image analysis when the image location is improved by whatever means. If points remain linked to their image origin, and the basis for locating that image is tracked, then updates can be automated. Is this capability being built into the GLIMS database? Hugh ----------------------------------------------------- Hugh H. Kieffer hkieffer@flagmail.wr.usgs.gov U.S. Geological Survey Phone 928-556-7015 2255 N. Gemini Drive FAX -7014 Flagstaff, AZ 86001 Main Office -7000 -----------------------------------------------------