Frequency-scanning interferometry is used for measuring test objects having multiple surface regions. The regions are distinguished and can be measured based on different measuring criteria. Interference data is gathered for the imageable portion of the test object from a plurality of interference patterns taken over substantially the same imageable portion at different measuring beam frequencies. The interference data is evaluated to determine topographical measures of associated points on the test object. The topographical measures are compared against a benchmark to distinguish between points on the test object that are within a first of the surface regions from points on a boundary separating the first surface region from one or more other surface regions of the imageable portion of the test object. The interference data of points within the first surface region are further evaluated to a higher accuracy.