Every corner in Corner-Plot gets a geolocated coordinate and a confidence rating — high, medium, or low. That rating comes from how many independent methods agree on the position and how authoritative each source is. Here are the five resolution methods, in order of reliability.
1. Surveyor-Stated Coordinates (Highest Confidence)
If the CP&F form contains a surveyor-stated latitude/longitude or SPCS coordinate, Corner-Plot uses it directly. This is the gold-standard source — it represents a licensed surveyor's field determination. The coordinate is accepted without cross-checking and flagged as surveyor_confirmed. Reconcile logic never overwrites it.
2. BLM CadNSDI PLSS Point Layer
The Bureau of Land Management's National Cadastral Survey Information System (CadNSDI) publishes authoritative PLSS point coordinates for all 30 PLSS states. These are the official cadastral positions, many of which were derived from original GLO field notes and subsequent dependent resurveys. Corner-Plot queries the state-specific CadNSDI WFS layer by GCDB point ID.
3. Cadastral Node Cross-Check
County GIS systems often publish their own cadastral parcel corners derived from recorded plats. These are independent of the BLM layer and make a strong corroborating source when they agree within a few feet. When both BLM CadNSDI and a cadastral node agree within the tolerance threshold, Corner-Plot raises confidence to high.
4. OSM Intersection Geocoding
For street_intersection monument class corners — monuments set at road intersections and described by the intersecting street names on the CP&F form — Corner-Plot geocodes the named intersection via the Nominatim API. This is authoritative for intersection corners where the record names the streets clearly (e.g., "Set at the intersection of Main St and Highway 20").
5. Sketch Road Offset (Lowest Confidence)
When no authoritative point is available, Corner-Plot reads the road and feature names extracted by OCR from the tie sketch diagram, geocodes those roads via Nominatim, and projects the corner using the bearing-and-distance ties from the record. This method is geometry-dependent and subject to OCR extraction quality — it earns medium confidence when the road geocodes resolve clearly, low confidence otherwise.
What the Confidence Ratings Mean
- High: Two or more authoritative independent sources agree within tolerance, or a single surveyor-stated coordinate is present
- Medium: One authoritative source resolves the position without corroboration
- Low: Only sketch-derived or centroid-fallback methods are available
A low-confidence coordinate still puts the corner in the right general area — typically within the correct section — but should be treated as an approximate starting point, not a recoverable position. In the field, start from the closest tie accessory and work inward.