Accuracy of Geographic Information

Objectives of lecture

• more announcements (change in lab schedule for next week)
• Data Quality and how to recognize it

Ways to handle accuracy

• Conformance to expectation (set some thresholds, producer decides)
• Truth in labelling; user makes the decision

National Map Accuracy Standards (as they were from 1947-97)

"90 % of well-defined points shall be within 1/30 inch of true location"

producer decides when and how to test. Results NOT shown...

"This map complies with NMAS"

Components of Data Quality

(beyond just "accuracy")

• Lineage
• Positional Accuracy
• Attribute Acuracy
• Logical Consistency
• Completeness

Testing

some examples (France, mostly)

How to read the data quality subtext on maps

Reliability diagrams, source data diagrams (charts and Army Map Service)

Lineage information (quads)

Explicit distinctions of reliability (PLSS lines on USGS quads)