----------------------------Original message---------------------------- I am in the process of implementing map projection software in an application under development and have come across an issue that doesn't affect physical maps. Many of the map projections which exist greatly reduce scale distortion when plotting map coordinates to physical media. Everyone knows that the Mercator projection wildly distorts the vertical axis - but by design. On the other hand, the oblique-stereographic projection has distortion as a function of deviation from the Standard Circle, Line of True Scale. The Standard Circle, which has a center point, which also happens to be the center point of the O-S map projection poses a dilemma for computer maps. What is the center of the map? As I said above, a physical map is fixed. But with software, all confusion is possible :). I can zoom and pan. Is the center of my map the visible center of my display? Or, do I tie it to the center of the original map? It's a rather minor distinction, but I'm curious as to how the professional map people's perspective. regards, --------------------------+------------------------------------------ Charles Gilley | All comments are my own... Senior Software Engineer -|- AEL/Cross Systems | Cross Systems - We make your radar 404-475-3633 | see double, triple, or more. --------------------------+------------------------------------------