For example, consider the case of a fault that has been offset by another. The geologist views the crosscutting fault as a singular object and the offset fault as a compound object consisting of two line segments. However, some GIS software packages place nodes at all line intersections. Consequently, both faults will be divided into multiple line segments, effectively creating two compound objects. Without some mechanism to 'reassemble' the crosscutting fault's segments back into a single feature, the geologic interpretation is obscured.
Similar problems occur with polygonal data.
Paper map constraints force geologic units to appear mutually exclusive, so that their cartographic representation reflects only that portion of the unit not covered by another. On a geologic map, a volcanic unit that underlies a sedimentary unit may appear as multiple, disjointed polygons where the sedimentary unit has eroded to expose it. Common symbolization, annotation, and accompanying cross-sections help inform the map user that the unit is contiguous at depth. Current database production practices typically digitize and attribute each polygon individually. Again, this fragmentation obscures the geologic interpretation that the individual exposures are really part of a single, underlying unit.