A method for measuring a height map of multiple fields of view on a surface of a substrate with an optical profilometer and combining them to a composite height map, the method includes: moving the profilometer relative to the surface from field to field along a route; measuring height maps of fields on the surface along the route with the profilometer; and, combining a plurality of height maps of measured fields by normalizing said height maps to each other to produce a composite height map of the surface; wherein the route is configured to minimize sensitivity to height drifting of the profilometer during combining a plurality of the height maps.