Neighbor Inherits Cabin From Old Lady, Then She Finds This Inside

Maps side by side

Suzan noticed they were maps depicting specific locations that did not make sense initially. But when she placed each map side by side, she realized it was the city where she and Magret lived. What did these maps mean? The maps were marked in multiple areas with a red pen as if Margret had tracked/researched this area for years. But why?