The contemporary 1:25,000 maps are a good starting point and at times, the 'best available or even the only option. They are great when intel has added German dispositions. The maps themselves usually contain a note that the contour lines may be inaccurate as indeed they were at critical moments. Examples included Hill 90 at les Hauts Vents, Hill 80 at Buron and Hill 30 that the 507th PIR was supposed to fall back to. None of these three existed. Hill 90 had a contour of only 70+, Hill 30 was one km further west (Shanley actually defending a 16 metre contour 'bump' on a generally downward slope), and Hill 80 at Buron was a flat plane. So contours should be corrected whenever possible with modern contour maps. With a word of caution. Sometimes these may experience 'local' disruptions whenever new highways are created. And in the Netherlands there may be new dykes, canals or even new land. Tricky bits them be. French maps are the easiest to do as a result of near contemporary aerial photos and current topographical maps of all of Normandy being readily accessible.