Features, Themes, and Layers

Features are things on the ground that we represent within a GIS. Features include trees, buildings, roads, streams, and mountains. Features also include things that we have designated on the ground but cannot be viewed such as state boundaries. Examples of features would be:

Arcata California This room The Pacific Ocean General Sherman (the tree) Eilean Donan castle Your house

A theme is a group of features of a similar type. Thus you could have a feature that is a road and then a theme that is roads for Humboldt County. Themes include:

Cities States Rooms Oceans Castles Houses Trees Countries

Images from Wikipedia, Public Policy of California, Dusky Wonder Site

 

Layers are typically of one theme (i.e. feature type) and are the main "chunk" of data that we work with in a GIS. When we load something from a file into a GIS, it is typically a layer containing data of one theme. A layer we might load into a GIS could be:

• A shapefile of cities for California
• A shapefile of state boundaries for the United States
• A shapefile with coastlines of the world
• A raster showing the elevations for Humboldt County
• A raster with temperature values for today for North America

Layers

Layer: A spatial dataset containing spatial and a-spatial data for a single feature type

Layers are stacked together within a GIS (Image from the USGS)

 

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