Objectives

In this section you will learn the basic terminology related to GIS software and analysis.

GIS Terms and Their Meanings:

Geocoding – The process of determining the coordinates of a specific location based on its street address or its existence within a known region. Coordinates can be assigned as a pair of XY coordinates or a latitude and longitude.

Centroid – The coordinates representing the center of a region. Generally there are two types of centroids:

Geographic Centroid – Represents the geometric center of the region. In the case of a circle or a square, the centroid will always be equidistant from the sides.

Population Centroid – Represents the point inside of a region containing the greatest population density.

Layer – Layers in a GIS system can be thought of as transparent overlays over the map, each containing a different type of geography. For example, typical layers in a map could include: highways, census tracts, patient locations, county boundaries, etc. By keeping them in separate layers, the lines and symbols used to depict the geographical features can be applied by layer to differentiate by color or line style, for example, census tract boundaries can be distinguished from zip code boundaries by using a different dotted versus solid lines.

Features – Geographic features are specific places on a map. Features can be addresses, roads, regions, etc.
Attributes – Attributes are literally database fields that describe geographic features. Each layer in a GIS can be thought of as table in a relational database. Attributes represent a database table which is linked to a geographic layer. Each record in the table corresponds to a geographic feature in the layer and its fields

Thematic mapping – Also sometimes called "theme mapping", it is a data visualization technique where the attributes of geographic features are displayed graphically on a map. For example, a map showing census tracts which are color coded on the basis of the number of households residing in each tract. Thematic maps can also be applied to point locations, such as a map showing hospital locations where the size, color, and symbol indicate the type of hospital and the number of beds

Projection – Since the earth is round and not flat, simple XY coordinates become inaccurate over longer distances due to the earth’s curvature. Projections are mathematical algorithms to adjust coordinates such as latitude and longitude for the curvature.

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