Arcmap Map Georeferencing techniques and keyboard shortcuts that save time. Make pyramids before georeferencing. ArcCatalog (or toolbox) can batch Make Pyramids. Choose the reference that you will use to georeference the map. For historic maps and older datums the coordinates that make up the margins of the map frame are often best. In the case of South American topo maps a UTM grid is available but I’ve found the edge Lat/Longs to be more versatile and quicker to reference. Put the map frame in the destination coordinate system/datum (read from edge of paper map). 1. Add the raster to Arcmap. Any raster that doesn’t have a worldfile can be re-referenced using the Georeferencing toolbar. If you have multiple rasters loaded sure that the right “Layer:” is selected or you might overwrite the existing georeference for another raster. 2. Zoom to approximately to size of the raster if you have a spatial reference (see Create Vector Grid in Hawth’s Tools extension for creating a reference grid). 3. Choose “Fit Raster to View…” from the Georeferencing menu 4. Choose a reference system and zoom in close to one corner. 5. Click on scan intersection and the right-click to “Add X,Y…” and type in the coordinates. I usually end up using decimal degrees. 6. The map probably moves quite a bit on your first georef point. Zoom to the Extent of the Raster to see all four corners again (Alt-click layer name). 7. Zoom in really close for georef point #2 (Z key). If possible go to the diagonally opposite corner from point 1 just to get it into the ball park for scale. 8. To go back out to the full raster view click the Previous View (big blue Left arrow). The Previous View arrow is available under the right-click menu. Alternately, with the keyboard you can do this by making sure the focus is on the data frame (F11) then typing < (Shift-,). 9. Zoom in close to place point #3 and point #4, repeating steps 7 and 8 above. 10. placing a fifth point somewhere in the middle of your raster (perhaps near your area of interest) considerably improves the accuracy. The fifth point is often slower than the four corner points, however, since the edge coordinates are not visible. This is a judgment call. 11. Choose "Update Georeferencing" to write out a worldfile. --- Recap: the quickest sequence I worked out was Fit Raster to view, zoom in really close to the top-left (Z key), georeference that one Alt-click raster layer name to zoom out view Z to zoom into Lower right corner, georeference it. Right click for Previous view arrow Z and zoom into top right, georef Right click for Previous view arrow Z and zoom into lower left, georef Update georef and select the next raster