The Zonal Statistics function

In a raster dataset, any two or more cells with the same value belong to the same zone. A zone can consist of cells that are connected or disconnected, or both. For example, all of the cells in a raster dataset with a value of 1 belong to a zone, all of the cells with a value of 2 belong to another zone, and so on. In fact, every cell in a raster belongs to a zone and a raster dataset can contain one or many zones.

In this graphic, there are six zones, but only one is delineated.

You use the Zonal Statistics function to find trends in data within zones defined by another raster or vector dataset. In this way, the areas of analysis are fixed or constrained by the shape and location of the zones. Instead of a new raster, the Zonal Statistics function produces a table of statistics and a graph.

The Zonal Statistics function requires a Zone dataset and a Value raster. Statistics are calculated by zone, not by cell. The results are presented as a table and a graph, not a new raster dataset.

Zones are composed of regions. A region is a group of connected cells in a zone. A zone that consists of a single group of connected cells has only one region.

Each zone is composed of at least one region. In this example, Zone 1 is composed of 3 regions, each of which is a different size and shape.