A Bar indicator over Map can help visualize data points (eg. user allocation) for any region of the map:
Moreover, heatmaps on different regions can convey more info like what regions have most open tasks to be worked on :
Also, the user can zoom into any region (by simply clicking on a region to zoom into that region on the map OR using google map style zoom at cursor position using mouse wheel or arrow keys) and visualize the user allocation in individual branches of that region:
Also, for allocating users to regions/branches, the manager can drag users to the region on the map OR select the regions in map for any given user.