What is an indirect spatial reference?

An indirect spatial reference is any way to describe a location without using coordinates. Indirect spatial reference methods usually use a geographic feature, such as a county, state, township or section of the Public Land Survey System, or a road, to uniquely identify a place. The reference may use the name of the feature (for example "Westmoreland County") or a code that identifies the feature (such as a county FIPS code). Other examples of indirect spatial references include street addresses, linear reference systems, and River Reach codes.

Why are indirect spatial references included in the metadata standards?

Indirect spatial references are included because they are a very common means by which observations or other attribute information are tied to a place. The location of many socioeconomic, environmental, and other data often are referenced by identifying a unit of political geography (e.g. a city, county, or state), census geography (e.g. block, block group, or tract), street address, linear referencing system (e.g. milepost), and so on. While these indirect spatial references alone may not be sufficient for geographic analyses, they can serve as a means to link the attribute data to coordinate descriptions of the places to which the attribute data apply.

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