I am attempting to generate a tile cache and then a tile package from multiple overlaid aerial imagery sources. The client software needs a tile package, and not a service, because it is for computer terminals on fire engines that need fast map drawing and don't have reliable, fast and fat cellular connections. It needs to be in Web Mercator. In the Manage Tile Cache tool, I set the Input Tiling Scheme to the ArcGIS Online scheme. Normally the resulting file is about 18 GB but when I recently added some imagery along the edge of the service area, it ballooned to 139 GB. What I added is actually smaller than the three existing sources, so I'm puzzling over why it balloons. My colleague noticed that the built-in ArcGIS Online scheme uses PNG, and suggested that I should set the output to JPEG instead. When I tiled this data before I used a custom scheme in Oregon State Plane North and set my own scales. My question is how can I get the Web Mercator scales in JPEG? I can't modify the existing Web Merc scheme. It appears the only way to get those scales and also be able to set the output format is to type the Web Merc scales by hand?