GIS Terminology

Map terms that you need to be familiar with in using web maps and services:

• Map Layer: A spatial dataset containing a common feature type. Layers are also referred to as coverages or themes.
• Active layer: The query, search, and identify tools all return data from the active layer. Only one layer can be specified as active at a time.
• Visible layer: Layers may be turned on or off. Visible layers will be shown on the map.
• Query: The process of selecting information from a GIS by asking spatial or logical questions of the geographic data. Spatial query is the process of selecting features based on location or spatial relationship (e.g., select all features within 300 feet of another; point at a set of features to select them). Logical query is the process of selecting features whose attributes meet specific logical criteria (e.g., select all polygons whose value for AREA is greater than 10,000 or select all streets whose name is 'Main St.'). Once selected, additional operations can be performed, such as drawing them, listing their attributes or summarizing attribute values.
• Identify: This function allows you to click on the map and have data returned about that feature of the active layer.
• Buffer: A zone of a specified distance around a selected feature. The resulting buffer zones form polygonal coverages.
• Pan: This function gives you the ability to manually move a map in any direction but does not change the map extent.
• Zoom: This function gives you the ability to change the map extent. You may zoom in or zoom out.
• Map Services: A map service is a grouping of layers. These layers typically will have a common theme. Map services may contain just one layer.