Agricultural Field Boundary Line Work

Presently, the  Agricultural Conservation Planning Framework  (ACPF) database has agricultural field boundaries for the states of Iowa and Illinois reflecting ground conditions in 2009. With a suite of new remote sensing products available for 2021, the GIS Facility at Iowa State University is seeking funds to update Iowa's field boundaries to 2021.

The agricultural field boundary lines are traced from a high-resolution color infrared image obtained from the  National Agriculture Imagery Program  (NAIP), as seen in the examples below. A  Cropland Data Layer  (CDL) is also used to evaluate land use within each field boundary.

In general, the basic GIS editing task is to delineate one kind of crop type within a single polygon. Delineating small waterways, large water bodies, and development are not a priority for the ACPF database, therefore they are usually not drawn unless they share a border with an agricultural field boundary. In the past, forested areas, pasture/grasslands and barren areas were also not a priority, but we have recently updated our digitizing methods to include these three land use types in the Iowa agricultural field boundary dataset for 2021.

For this demonstration, accuracy and precision are used to describe errors and correctness in the field boundary editing process.

Accuracy is defined as how close the digitized lines are to the actual boundaries on the NAIP image; that is to say, are the lines close to the correct location? If so, these lines are considered to be of “High Accuracy.”

Precision is defined as when the digitized lines surround the correct land use, and the field boundaries have been reasonably traced to match the land use seen on the NAIP image and on the Cropland Data Layer. These lines are considered to be of "High Precision."

Older agricultural field boundaries exhibit low and high accuracy and low precision. Using updated methods and GIS technology, the desired result is to produce agricultural field boundary lines that have both high accuracy and high precision.

Below are examples of editing errors and required corrections. These are best viewed using your full screen and by clicking to the right to advance through the slideshows.