It would be good to predefine a fix scale which results in different pages sizes for the single maps. I would like to generate maps for administrative units which are very different in shape and size but the resulting maps must all have the same scale so that the paper sizes are very different. That means that the paper size must be driven by the scale and not the other way round. I should be able to select the feature class containing the administrave units (polygons), choose a fix scale and ArcGIS should automatically create the right paper size.
