NMBGMR Draft Geologic Data Model - v. 1.0.3
Topology

Overview

Topological rules define the spatial relationships between feature classes and the constraints within particular feature classes. For instance, geologic contacts must bound polygons of a particular lithologic unit. Likewise, contacts cannot have dangles (end in space). These rules are encoded in the geodatabase and ensure consistency and data integrity.

Cluster Tolerance

Two (or more) points or vertices are considered to be coincident in the geodatabase if the distance between them is less than the cluster tolerance. The cluster tolerance chosen should be dependant on the accuracy of the data. For geologic maps, most data is unlikely to be positioned at an accuracy greater than that of a handheld GPS -- 3 meters at best with WAAS. However, differential GPS positioning can be considerably better. For now a cluster tolerance of 0.01 meters will be used. Points positioned by high-precision GPS should either not participate in the topology (and therefore not be affected by the cluster tolerance) or should have a higher rank in the topology.

Ranks

Each feature class that participates in the topology is relatively ranked based on accuracy. When points or vertices are adjusted because they fall within the cluster tolerance, the point with the lower rank will be moved (1 is the highest rank).

Feature Classes that participate in the topology and their ranks:

• Map_Extent_poly (rank=1) -- the map extent should never be adjusted
• Map_Boundary (rank=2) -- the map boundary should never be adjusted
• Fault_point (rank=3) -- if stations are recorded with GPS they shouldn't be adjusted, if not, they can be snapped to the line during digitizing.
• Fold_point (rank=3) -- as above
• Lith_Contacts (rank=4)
• Fault_line (rank=4)
• Fold_line (rank=4)
• Lith_poly (rank=4)
• Lith_poly_label (rank=4)

Rules (* these rules should be valid before building polygons)

Contacts:

• *Lith_Contacts — no dangles.
• *Lith_Contacts — no intersections.
• *Lith_Contacts cover the boundary of Lith_poly features.

Faults:

• Fault_point is covered by the Fault_line feature class (exceptions allowed when minor fault data is not on a mapped fault: MappedFeature = FALSE).
• *Fault_line - no intersections.

Folds:

• Fold_point is covered by the Fold_line feature class (exceptions allowed when minor fold data is not on a mapped fold: MappedFeature = FALSE)

Geologic Units (Lith_poly):

• Lith_poly — no overlap.
• Lith_poly — no gaps.
• Lith_poly covers the Lith_Contacts feature class.
• Lith_poly contains Lith_poly_label feature class.

Map Boundary/Extent:

• Map Boundary polyline is covered by the Lith_poly feature class.
• Map Boundary polyline is covered by the MapExtent polygon feature class.
• MapExtent polygon boundary must be covered by Map Boundary polyline.