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3.4 Logical Consistency

A report on logical consistency must describe the fidelity of relationships encoded in the data structure of the digital spatial data. The report must detail the tests performed and the results of the tests.

3.4.1 Tests of Valid Values.

Tests for permissible values may be applied to any data structure. Such a test can detect gross blunders, but it does not ensure all aspects of logical consistency.

3.4.2 General Tests for Graphic Data.

A data base containing lines may be subjected to the following general questions:

• Do lines intersect only where intended?
• Are any lines entered twice?
• Are all areas completely described?
• Are there any overshoots or undershoots?
• Are any polygons too small, or any lines too close?

Different tests may be applied to address these questions, but the quality report must contain a description of the tests applied or a reference to documentation of the software used. The report must state whether all inconsistencies were corrected or it must detail the remaining errors by case.

3.4.3 Specific Topological Tests.

For exhaustive areal coverage data transmitted as chains or derived from chains, it is permissible to report logical consistency as "Topologically Clean" under the condition that an automated procedure has verified the following conditions:

a) All chains intersect at nodes. Use of exact case or tolerance must be reported.

b) Cycles of chains and nodes are consistent around polygons. Or, alternatively, cycles of chains and polygons are consistent around nodes.

c) Inner rings embed consistently in enclosing polygons.

The quality report must identify the software (name and version) used to verify these conditions.

3.4.4 Date of Test.

The report must include the date on which the tests were applied. If corrections and modifications have occurred after the test for logical consistency, the quality report must indicate how the new information was checked for logical consistency.