Autodesk 15606-011408-9330 User Guide - Page 181

Joint Photographic Experts Group (JPEG) A format for compressing raster images that offers a compression ratio of up to 20:1. Note that some image information is lost when a raw image such as TIFF or BMP is converted to JPEG format. JPEG See Joint Photographic Experts Group. key An alphanumeric character string or an integer used to uniquely identify a map feature or a record in an attribute table. If a spatial feature in an SDF and a record in an attribute table use the same key, they are linked, so you can select that spatial feature and retrieve the data in that record. This is useful for generating reports because you can select the spatial features you want and then generate a report containing the attribute data for those features only. Keys must be unique; if more than one spatial feature or record uses the same key, the links between the spatial features and the attribute data do not work. Note that for an SDF and for OLE DB providers linked to an SDF, the key must be a string. See also primary key. latitude/longitude system A global coordinate system in which locations are expressed by geographical coordinates (the geodetic latitude and longitude) that depict angular measurements relative to the Earth's ellipsoid. These coordinates are often expressed in decimal degrees or degrees° minutes' seconds". See also arbitrary XY coordinates. layer See map layer. layer group A collection of related map layers. You create layer groups in Autodesk MapGuide Author. legend A key to or an explanation of the symbols in a map, and their meaning or values. In the View tab of the Autodesk MapGuide Author Map Explorer and in Autodesk MapGuide Viewer, you can use the legend to turn layers on and off so that the map features they contain are no longer visible or selectable. line A drawing entity with start and end coordinates connected by a single straight line. Lines typically represent the shape of map features too narrow to be displayed as an area at the given scale (contours, street centerlines, or streams), or linear features with no area (county boundary lines). line spacing ratio The ratio of the distance between lines of text to text character height. For example, if the distance between lines of text is 10 mm, and the line spacing ratio is 0.5, the font height is 20 mm. linetype A property of a line that defines its appearance. Examples of linetypes include continuous, dashed, and dotted. linked table or database A table or database linked to a layer using Autodesk MapGuide Author. The records in the table are linked to the spatial features in the layer via common keys. map An abstract representation of the physical features of a portion of the Earth's surface graphically displayed on a planar surface. Maps display signs, symbols, and spatial relationships among the features. They typically emphasize, generalize, and omit certain features from the display to meet design objectives. For example, railroad features might be included in a transportation map but excluded from a highway map. map feature Any spatial feature on a map. In the Autodesk MapGuide products, map features can be points, polylines, polygons, or text. Although raster images are technically not map features, you can display them in raster layers. Glossary | 181