Many products have been developed using various geometrical shapes to stratify the Earth’s surface. One program focused on developing grid products is the Environmental Monitoring and Assessment Program (EMAP) that was run by the Environmental Protection Agency. EMAP grids are composed of tessellated equal-area hexagons. Different cell size products are available.
EMAP hexagon products do allow for scaling up of data from several different locations (i.e., local site, state, bioregion, continent). EMAP is built upon a probability-based sampling design , and it takes samples at regular intervals starting with a randomly selected location.
EMAP hexagon products of different cell sizes do not nest within each other, which is important for spatial sub-sampling. Also, many potential grid users have indicated that they are only interested in using square cells because hexagons can be difficult and expensive to delineate on the ground.
Examples of use
EMAP products have been used by the USGS Gap Analysis Program and USDA Forest Service Forest Inventory and Assessment Program, among others. The National Marsh Bird Monitoring Program (http://ag.arizona.edu/srnr/research/coop/azfwru/NationalMarshBird/) uses the EMAP grid as the basis for its flexible sampling framework that allows for inferences at multiple spatial scales.
For more information
Sampling Grids >