The present disclosure shows creating a first layer and a second layer, in computer memory and substantially overlapping at least a segment of line from said first layer with at least a segment of another line from said second layer. A first non-dimensional attribute is different from said second non-dimensional attribute of the two lines. A user length field enabling a client with said interactive file to override at least one of said length numeric values, where said area operator may automatically recalculate area based on said length field override is shown. Also, providing a visual marker that is moveable on said computer monitor around said aerial imagery region, which may be moved, to more precisely identify the location of the building roof structure is shown.