Feature Class

A feature class is Esri's name for a table of geographic features that all have the same kind of shape and the same fields. Esri's ArcGIS Pro documentation defines feature classes as "homogeneous collections of common features, each having the same spatial representation (such as points, lines, or polygons) and a common set of attributes." It adds: "The four most commonly used feature classes are points, lines, polygons, and annotation."

One row is one feature. The shape column holds its geometry, and the other columns hold its attributes. A feature class lives in a geodatabase, either on its own or inside a feature dataset, which Esri says is used "to spatially or thematically integrate related feature classes." See Geodatabase.

Rules a feature class can carry

• Domains: a list or range of valid values for a field. Esri says "Domains help ensure the integrity of your data."
• Subtypes: subsets of one feature class that can follow different rules.
• Topology: in Esri's words, "Topology allows you to create rules to enforce how features behave when they share the same location or boundary."

BLM's layers are feature classes

BLM describes its national PLSS web service as "a compilation of feature classes designed to represent the Public Land Survey System (PLSS) grid." Its section layer holds "the sections and other types of divisions that divide the PLSS Townships." The township layer's fields include the principal meridian (PRINMER), the township number and direction (TWNSHPNO, TWNSHPDIR), and the range number and direction (RANGENO, RANGEDIR).

BLM's "Mining Claims Not Closed" layer from MLRS is a polygon feature class too; its metadata lists it as an "Enterprise Geodatabase Feature Class." Its fields include the case serial number (CSE_NR), the legacy LR2000 case serial number (LEG_CSE_NR), and "Record Acres of the Case" (RCRD_ACRS).

Size limits

Esri lists the file geodatabase limits for a feature class as 65,534 fields and 2,147,483,647 rows, with a default size limit of 1 TB. A shapefile holds a single set of shapes of one type, with much tighter limits. See Shapefile.

Why it matters in mining claim research

Mining claim work combines several feature classes: mining claim polygons, PLSS townships and sections, land status, and withdrawals. Each has its own geometry type, fields, and coordinate system, and each field means only what its metadata says. RCRD_ACRS, for example, is the record acreage of the case, which is a different thing from the area a GIS computes from the polygon. Reading the field definitions first keeps a recorded number, or a quarter-section outline, from being mistaken for a measured boundary.