First, select the 2up button on the top menu bar (not available in all collections).
Now select the two maps you wish to view - the selection process varies between collections:
Select Basemaps using the button on the map window for Ordnance Survey, Geology Roam, Environment Roam, Verisk Roam.
Select decades with the Timeline in Historic Roam.
Select different features in Map Content in Marine Roam (no basemaps available)
Change opacity of maps in Aerial Roam.
Note: In the collections where Map Content is available, you can select features in the map you are viewing on your left with the Map Content tool. You cannot select features in the map you are viewing on the right.
Historic Roam example
In this image, historical maps of Nottingham from different decades are compared.
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