Hi, I just have one small point to add to Martin's answer.
Map projections convert Lat/Long to a planar coordinate system that we can easily do calculations on (distance, area, etc.). However, a map projection ends up distorting either area, direction, distance or shape (I think that is the full list). So if you want to calculate areas, you should chose a map projection that preserves area (though it might distort other properties). For example, the Mercator projection was created to preserve direction, but completely distorts area (checkout Greenland on a Mercator map). Also, note that any projection will distort properties more as you get away from their central meridian (or latitude of origin). So projection parameters for Canada do not work very well for Europe. For example, the Mercator (usually with a latitude of origin at the equator) will distort greenland much more than shapes near the equator. There is a bit more information (in serious need of an edit) here: http://www.geotools.org/display/GEOTOOLS/Introduction+to+Coordinate +systems Rueben On Wed, 2006-11-01 at 12:32 -0800, todd runstein wrote: > I'm still very new to GIS - hence the newbie style > question. > > Suppose I'm using EPSG:4326, and I have the two > coordinates -122:40 and -120:42. It would seem > reasonable that because -122-(-120)=-2 and 40-(42)=-2, > I have a proper square (something that would fit > nicely in a 500px X 500px window). Following this > logic, -122:40 and -120:43 would fit in a 500px X > 750px window. > > However, I realize that because the planet isn't flat, > I may be making assumptions that aren't correct. I've > read some articles on projection, but I'm still not > comfortable enough to determine whether I'm > understanding all of this correctly. > > Could someone shed some light on this for me? I'll > probably have some follow up questions, so patience > and understanding are appreciated. > > Todd > > The only "dumb question" is the one you were too afraid to ask. ------------------------------------------------------- This SF.net email is sponsored by: Splunk Inc. Do you grep through log files for problems? Stop! Download the new AJAX search engine that makes searching your log files as easy as surfing the web. DOWNLOAD SPLUNK! http://ads.osdn.com/?ad_id=7637&alloc_id=16865&op=click _______________________________________________ Geotools-gt2-users mailing list [email protected] https://lists.sourceforge.net/lists/listinfo/geotools-gt2-users
