The key to interoperable map services is the ability to
portray adjacent maps using the same symbolization scheme such that when the
maps are displayed, the visual discontinuity at the boundary is minimized.
Because of the discrepancies in mapping interpretation and intention, there are
commonly discontinuities in the definition of map units between geologic maps
produced by different authors or at different times. These discontinuities
cannot be avoided, and resolving them is a compilation process that will often
require additional field work; this is outside the scope of service deployment.
What can be avoided is visual discontinuity related to portrayals based on
different classification schemes on adjacent maps. Map unit classification
schemes for regional geologic maps typically define units based on some
combination of age, genesis, and lithology. The larger the area over which the
scheme is meant to apply, the more generalized the definition of the units must
be.
