Zonal Statistics

Definition

Zonal statistics is a geostatistical method used in geographic information systems (GIS) to extract statistical information from raster datasets within specified vector-based zones. These zones are areas that share a common characteristic or defined boundary, such as political boundaries, ecological regions, or land use areas. The technique is particularly beneficial for analyzing spatial patterns and relationships within the specified zones by summarizing the underlying raster data.

What is Zonal Statistics?

Zonal statistics functions by overlaying a vector layer, which contains the zones of interest, on top of a raster dataset. The raster dataset typically contains continuous data like elevation, temperature, or precipitation. The zonal statistics tool calculates specific statistics, such as sum, mean, range, minimum, or maximum, of the raster data covered by each zone. This provides insights into the distribution and patterns of the data within each defined boundary.

For example, zonal statistics can be used to find the average rainfall in different municipalities, determine the maximum temperature in various climate zones, or calculate the total population within certain administrative boundaries. By summing, averaging, or identifying the range, minimum, or maximum values within the zones, users can derive meaningful metrics that inform decision-making processes, policy development, or research initiatives.

FAQs

What types of data are used in zonal statistics?

Zonal statistics requires a vector layer to define the zones and a raster dataset containing the data to be analyzed. The vector layer typically consists of polygons, but can also involve points or lines, while the raster data often represents continuous variables like elevation or temperature.

How is the polygon boundary handled in zonal statistics?

During the calculation of zonal statistics, the tool evaluates each cell of the raster data to determine its inclusion within the polygon boundary. Depending on the specific software and settings, cells that intersect with the boundary may contribute proportionally or entirely, based on their overlapping area with the polygon.

Can zonal statistics be used with non-spatial data?

No, zonal statistics are a spatial analytical method that relies on spatially referenced data. The technique necessitates the involvement of geographic boundaries (zones) and spatially continuous data (raster) to derive the relevant statistics.