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Tuesday Term of the Week: Overlay

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There are many benefits to digital mapping. It gives users the ability to compare different kinds of information at one time. One of the ways this works is through overlay, a spatial operation in which two or more map layers at a common scale and coordinate system are superimposed, either digitally or on transparent material, for the purpose of showing the relationships between features that occupy the same geographic space. This is a vital technique when analyzing land and property assessments. Individual geographic features can be completely contained within other features, or can partially overlap one another. The area of overlap creates a composite region made from the intersection of the features. Map symbology is also considered an overlay, containing informational items like a legend, feature labels, icons, scale bars, coordinate grids, direction arrows and colors or fill patterns. Symbology is typically placed on top of the other map layers.