Most of our local datasets are in GCS_NAD_1983. When I add an ESRI Base Map to a map project that has one of my NAD83 datasets, I naturally get the warning that they are in GCS_WGS_1984. I know these two coordinate systems are similar, but what I'm wondering is whether it would make my ArcMap run faster when using ESRI Base Maps if I converted my datasets to GCS_WGS_1984 because the software wouldn't have to calculate "projecting on the fly"? We also have many users using our datasets in desktop ArcGIS Explorer but I often get complaints that ArcGIS Explorer runs very slow/crashes a lot, so I'm wondering if part of that issue is AGX having to reproject on the fly to align our NAD83 data with the WGS84 base maps. I really don't look forward to reprojecting our vast catalog of data to match the Base Maps, but if that is going to significantly improve performance, I might look into it. Any thoughts or advice on whether this might be a problem and worth the effort of reprojecting our data to WGS84? Thank you, Jon
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