Data Quality Information
Functional Diagram
Attribute Accuracy
exampleLogical Consistency Report
A:A report on logical consistency shall describe the fidelity of relationships encoded in the data structure of the digital spatial data. The report shall detail the tests performed and the results of the tests.
Test 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.
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 shall contain a description of the tests applied or reference to documentation of the software used. The report shall state whether all inconsistencies were corrected or it shall detail the remaining errors by case.
Specific Topological Tests: For exhaustive area coverage data transmitted as chains or derived from chains, it is permissible to report logical consistence 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 shall 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 shall identify the software (name and version) used to verify these conditions.
Date of Test: The report shall include the date on which the tests were applied. If corrections and modifications have occurred after the test for logical consistency, the quality report shall indicate how the new information was checked for logical consistency.
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Completeness Report
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Positional Accuracy
A:The quality report portion on positional accuracy shall include the degree of compliance to the spatial registration standard (see section 4.1.3.5 of SDTS). Quality of control surveys shall be reported by using the procedures established in the geodetic standard. If a separate control survey has been used, it shall be described in the standard form, even if results fall below the recognized classification thresholds.
Descriptions of positional accuracy shall consider he quality of the final product after all transformations. The information on transformations forms a part of the lineage portion of the quality report.
The report of any test of positional accuracy shall include the date of the test. Variations in positional accuracy shall be reported either as additional attributes of each spatial object or through a quality overlay (reliability diagram).
Measures of positional accuracy may be obtained by one of the following optional methods.
Deductive Estimate: Any deductive statement based on knowledge of errors in each production step shall include reference to complete calibration tests and shall also describe assumptions concerning error propagation. Results from deductive estimates shall distinguished from results of other tests.
Internal Evidence: Federal Geodetic Control Committee procedures will be used for tests based on repeated measurement and redundancy such as closure of traverse or residuals from an adjustment.
Comparison to Source: When using graphic inspection of results (‘check plots’), the geometric tolerances applied shall be reported and the method of registration shall also be described. Use of check plots shall be included in the lineage portion.
Independent Source of Higher Accuracy: The preferred test for positional accuracy is a comparison to an independent source of higher accuracy. The test shall be conducted using the rules prescribed in the ‘ASPRS Accuracy Standards for Large Scale Maps’ (see section 1.3.3. of SDTS). When the dates of testing and source material differ, the report shall describe the procedures used to ensure that the results relate to positional error and not to temporal effects. The numerical results in ground units, as well as the number and location of the test points, shall be reported. A statement of compliance to a particular threshold is not adequate in itself. This test may only be applicable to well-defined points.
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Lineage
A:The lineage portion of a quality report shall include a description of the source material from which the data were derived and the methods of derivation, including all transformations involved in producing the final digital files. The description shall include the dates of the source material and the dates of ancillary information used for update. The date assigned to a source shall reflect the date that the information corresponds to the ground; however, if this date is not known, then a date of publication may be used, if declared as such.
Any data base created by merging information obtained from distinct sources shall be described in sufficient detail to identify the actual source for each element in the file. In these cases, either a lineage code on each element or a quality overlay (source data index, etc.) shall be required.
The lineage portion shall also include reference to the specific control information used. Control from the National Geodetic Reference System shall be identified according to identifiers in that system, while other points used for control shall be describe with sufficient detail to allow recovery.
The lineage portion shall describe the mathematical transformations of coordinates used in each step from the source material to the final product. The locations of any registration points for coordinate transformations shall be given. The methods used to make coordinate transformations shall be documented. To fulfill this standard, it is acceptable to make reference to separate documentation for the coordinate transformation algorithm used, but the specific parameters applied shall be described for the particular case. Documentation of a transformation algorithm shall include the nature of computational steps taken to avoid loss of digits through roundoff and shall include a set of sample computations, including numerical values of coefficients, to confirm equivalence of transformations. The documentation of a transformation algorithm shall be available on request by a user obtaining digital data even if that user is not licensed to use the particular software.
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Cloud Cover
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