I havn't been able to find this in ant FAQs I know about. Please point me at the right one if there is one. I've been working with digital maps for some years, but I find it quite hard to track down explinations of the various Lat Long systems and how they relate. I know that is I use a map from Sweden that the Prime Meridian does not go through the same place as a British map. But when it comes to Lat Long shifts between datums, things get cloudier. I can see that a change from a non-geocentric ellipsoid to a geocentric one can affect Lat and Long for a given position on the surface of the Earth. I'm pretty sure that changing between two geocentric ellipsoids will only affect Lat for a given position on the surface of the Earth. (Is that correct?) But I'm not sure when all these other Lat Long systems that are defined in MapInfo come into use. I'm used to being able to find the projection used, and usually the datum on maps I'm working with. Or select a suitable projection if I'm compiling from various sources. But I'm not sure how much difference the different Lat Long systems make - how bad is selecting the wrong one for instance? Any help with this, or a pointer to a Web page covering this would be most appreciated. If there isn't already a Map Projection FAQ perhaps this would be a good starting point. Cheers, John Harrop ([EMAIL PROTECTED]) Cyberquest Geoscience Ltd - Mineral Exploration Fieldwork - Computer Geology ---------------------------------------------------------------------- To unsubscribe from this list, send e-mail to [EMAIL PROTECTED] and put "unsubscribe MAPINFO-L" in the message body, or contact [EMAIL PROTECTED]
