Slashgeo

Henry wrote to me: "Henry Bottomley's Java applet for world map projections allows a quick real-time view of the distorting effects of 15 different projections as well as altering the center and orientation of the map. It has just been extended to do the same for the Moon, Mars and even Jupiter." The java code is also available on the website.

SharpGIS offers a nice generic entry on spatial references, coordinate systems, projections, datums and ellipsoids. Even if this is things you already know, I'm sure some of your colleagues could benefit from reading it. ;-) From the text: "[...] coordinate systems are that they are all relative to the center of Earth and except the Geocentric coordinate system, uses a height system relative to the surface of the earth. This poses two immediate problems: * Where is the center of the earth * What is the shape of the earth? [...] A common statement that I hear in GIS is the following “My map doesn’t have a projection”, but this is simply not possible (unless you have a good old globe). Often people are referring to data that is in longitude/latitude and displayed on a map without applying any projection. What happens is that the system applies the simplest projection it can: Mapping Longitude directly to X and Latitude to Y. This results in an equirectangular projection, also called the “Plate Carree” projection."

Kurt's Weblog links to the Spatial References website, which lists projections information in various formats. In addition to seeing existing EPSG codes, users can submit their own projections. Information for projections are translated in GML, Proj4, ESRI WKT, OGC WKT, USGS and JSON. Comments about the projections can also be shared. See also related stories below.