Established in 1812, the federal General Land Office (GLO) was charged with surveying public lands belonging to the federal government, and then conveying these lands to state or private ownership. Land surveyors, under contract with GLO, were required to follow specific survey instructions. These methods were developed first for Ohio in 1785, and refined over the decades as federal land surveys progressed westward to the Pacific Coast. The surveys created the familiar rectangular grid of townships and ranges, now called the Public Land Survey System (PLSS), that covers 30 states. In 1946, the GLO was merged with the U.S. Department of the Interior's Grazing Service to form the Bureau of Land Management (BLM).

The GLO surveys created a more or less consistent dataset spanning 200 years and covering nearly 1.5 billion acres. Since the 1920s, ecologists, historians, and others have used GLO records as a source of information on landscape condition and settlement as seen at the time of survey:

•  Land surveyors routinely use historical GLO data because it is the foundation of all land ownership records, and all land survey lines are interconnected.

•  Ecologists and Botanists use GLO survey lines as a grid of transects, along which surveyors recorded changes in vegetation, and information about trees and shrubs every half mile. They also had to record information at random points where lines intercepted trees, rivers, streams, lakes, and other natural features. Notes on streams and rivers often included depth, current, alluvium, and condition of the banks. Witness tree data are particularly useful in assessing historical stand density, fire history, and species distributions. They are being used to restore plant community structure, species composition, and ecological processes.

•  Historians use the GLO grid in a similar way to ecologists, because surveyors were required to record where lines intercepted man-made features such as roads, fencelines, farmyards, and towns. Surveyors routinely recorded distances and compass bearings to prominent buildings that were visible along the survey lines. These records have been used to relocate early settlements, support claims to water rights, and validate early census records. GLO users of any stripe also often are drawn to its history because they inevitably wonder who the surveyors were, what they saw, and how they did their work without roads, electronic survey equipment, chainsaws, and even maps.

The landscape described in GLO notes has often erroneously been called "presettlement," implying pristine ecosystems untouched by human hands, but in most places surveyors saw lands shaped by at least 10,000 years of occupation and management by native peoples.

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