Features

Typically, a feature in ArcGIS is a representation of a real-world object on a map that is tied to a row in a table of an ArcGIS-supported database format. A road is an example of an ArcGIS feature.

Examples of military features in ArcGIS are infantry platoons and axis of advance main attack arrows.

Feature and geodatabase basics

To fully understand the meaning of feature in ArcGIS, you must understand a bit about geodatabases and the relationship between feature classes and maps.

The database table containing the row mentioned above is known as a feature class in ArcGIS. For example, one row in the feature class might be an infantry platoon named 1st Platoon. A second row might be an infantry platoon named 2nd Platoon.

ArcGIS-supported databases are typically referred to collectively as geodatabases, and they include file geodatabases, Microsoft Access databases, and multiuser relational DBMSs (such as Oracle, Microsoft SQL Server, PostgreSQL, Informix, or IBM DB2).

The data (the tables—the feature classes) in a geodatabase is one of two main components of ArcGIS. The other main component is the map. The map (an .mxd file for ArcMap maps, for example) contains information on how to display data stored in a geodatabase. A map does not contain geodatabase data; a map does, however, contain references to geodatabase data via the map's layers. Maps and data are distinct entities.

The relationship among maps, layers, and feature classes

Maps contain information such as the layout of the map and which layers you want to include in the map. Layers contain additional visualization information. This is why you'll encounter discussions of ArcGIS as being separated into two categories: visualization (maps and layers) and data.

A layer in an ArcGIS map points to a feature class in a geodatabase. The layer contains information about how you want to display that feature class in a map, such as what symbols you want to use for the features in a feature class or which fields in the feature class are visible on the map.

A single feature class can be referenced (can appear in) many maps. It can even be referenced within the same map as different layers, when you want two different renderings (visualizations) of the same data. This one-to-many relationship should underscore the lesson that layers and data are distinct entities. Layers help you help your map readers visualize the data, or underlying data, as it is sometimes called. To view the data underlying a layer in ArcMap, right-click the layer and click Open Attribute Table.

Common layer/feature class types are points, lines, and polygons. The layer and feature class in the pairing must be of the same type (point, line, polygon, and so on). A point type of layer or feature class must contain only point features; a line layer must contain only lines, and so on. Generally speaking, the coding scheme (the position 1 value of the SIDC) a military feature has or the category (warfighting, tactical graphic, and so on) a military feature is listed under in the military specification is what determines which type of layer/feature class (point, line, and polygon) the feature must live in in ArcGIS. For details and information on other factors that determine the layer type, see Identifying which layer to use for a feature.

For ArcGIS for Desktop products (as opposed to clients using feature services and editing capability), to change data stored in the feature class, you must edit the feature class in an edit session in ArcMap. To change the table schema, you can edit the feature class in ArcCatalog or ArcMap.

Esri military feature layer packages simplify your job of adding military features to a map because they contain the table schemas, feature templates, symbology, cartographic representations, geometric effects, unique values layers, and label properties designed for the symbols listed in military symbol specifications supported by ArcGIS. For details on how unique values layers are used, see Military operations points. For details on how representations and geometric effects are used, see Military operations lines and areas.

When you save a map, you are essentially saving visualization information only. When you save edits in an edit session, you are saving changes to the underlying data—the feature class or feature classes you were editing.