Geocoding

Geocoding turns a written location into a place on the map. The U.S. Census Bureau's Geocoding Services API documentation defines it: "Geocoding is the process of taking an address and returning an actual or calculated latitude/longitude coordinate."

Address geocoding

The Census Geocoder accepts "a single address, batch of up to 10,000 addresses, or location coordinates." Its results come from address ranges in the Bureau's MAF/TIGER database, and the Bureau is direct about what that means:

• "Address ranges within TIGER include all possible structure numbers even though actual structures may not exist."
• "Coordinate results are interpolated, or approximated, based on the physical location that the address geocoded on the TIGER address ranges."
• It "only geocodes addresses that are within the United States, Puerto Rico, and the U.S. Island Areas."

Going the other way, the Bureau says geography results "can also be obtained directly by searching on the latitude/longitude coordinates."

Legal description geocoding

Mining claim cases in BLM's records are located by legal land description, not by street address. BLM's MLRS mining claim geometries "are primarily derived from Legal Land Descriptions (LLD) for the case and geocoded (mapped) using the Public Land Survey System (PLSS)." BLM gives each case a data quality score, grouped into seven classes:

1. Direct PLSS Match
2. Calculated PLSS Match, "a best guess based on the underlining PLSS"
3. Mapped to Section
4. Combination of mapped and unmapped areas
5. No NLSDB Geometry, Only Attributes
6. Mapped to County
7. Improved Geometry, cases whose geometry was "edited by BLM staff"

BLM also says "Geospatial representations might be missing for some cases that can not be geocoded using the MLRS algorithm."

Why it matters in mining claim research

A geocoded point or polygon is only as good as the description and the match. A mining claim mapped to a whole section, or to a whole county, is on the map but not located. Before a mining claim polygon is used for overlap or acreage, its quality score should be read, and anything short of a direct PLSS match treated as approximate. Even a direct match shows the quarter section. The staked boundary, BLM notes, is in the accepted notice or certificate of location in the official case file. See Spatial Data.