Glossary: Glossary

Glossary

ArcInfo: a geographic information system software product that is developed and supported by ESRI.
area: a type of map feature that represents a closed (polygonal) area such as a state or county. Area boundaries are defined by individual line segments. An area can also be the size or extent of the enclosed polygon as calculated by the GIS procedure. See also perimeter.
area layer: a layer that contains the regions, such as census tracts or ZIP code zones, that are part of a map. See also area.
attribute data: values that are associated with features on a map. Attribute data is linked to map features by key variables. Attribute data can include information such as household incomes, population, sales revenue, ages, and so on. See also spatial data and key variable.
chain: a sequence of two or more points in the coordinate space. The end points (that is, the first and last points of the chain) are called nodes. See also detail point and node.
coverage: a subset of the spatial data that is available to a map. For example, a coverage might include the spatial data for a region of a map that is contained in a spatial database.
coverage entry: a SAS catalog entry of type GISCOVER that defines the subset, or coverage, of the spatial data that is available to a map.
data type: an attribute of every column in a table or database. The data type tells the operating system how much physical storage to set aside for the column and specifies what type of data the column will contain. It is similar to the type attribute of SAS variables.
data value: a unit of character or numeric information in a SAS data set. A data value represents one variable in an observation. For example, the variable LASTNAME might contain the data value Smith.
database management system: a software application that enables you to create and manipulate data that is stored in the form of databases. Short form: DBMS.
DBMS: See database management system.
detail point: an intermediate point that delineates the interior segment of a line. Detail points are those points on a line between the from-node and the to-node. See also point, to-node, and from-node.
DLG: Digital Line Graph. A data exchange format for planimetric data. DLG was developed by the United States Geological Survey (USGS).
DXF: a data exchange format that is widely used in computer-aided design (CAD) applications.
Dynamap: spatial (map) data that is developed and supported by Tele Atlas NV.
external file: a file that is created and maintained by a host operating system or by another vendor's software application. SAS can read data from and route output to external files. External files can contain raw data, SAS programming statements, procedure output, or output that was created by the PUT statement. A SAS data set is not an external file. See also fileref.
feature: a man-made or natural physical object such as a river, utility line, school, street, or highway; or an intangible boundary or area such as a sales territory, a census tract, a county boundary, or a state boundary.
feedback area: an area in the GIS Map window that displays information about the map scale, as well as about location coordinates, distance values, and attribute values.
fileref: a name that is temporarily assigned to an external file or to an aggregate storage location such as a directory or a folder. The fileref identifies the file or the storage location to SAS. See also libref.
from-node: the starting coordinates of a line segment on a SAS/GIS map. See also detail point, node, point, and to-node.
generic import file: a file that contains spatial data that you can import by writing a SAS DATA step to convert the data to a SAS/GIS generic form. Once the data is in this generic form, SAS/GIS software can finish the import process.
geocoding: a process for calculating an X and Y coordinate for a street address.
geographic information system: a software application for organizing and analyzing data that can be referenced spatially - that is, data that can be associated with physical locations. Many types of data, such as data from marketing surveys and epidemiological studies, have a spatial aspect. Short form: GIS.
GIS: See geographic information system.
key variable: a variable that is used to associate attribute data with specific features on a map. The key variable has the same data type (character or numeric) and the same data value in the spatial database as in the attribute data set.
label data set: a data set that defines the attributes (location, color, size, and so on) of labels that will be displayed on a map.
layer: a group of features that have the same attribute. For example, all of the lines that are streets, all of the points that are houses, and all of the areas that are census tracts are layers. See also static layer and thematic layer.
layer definition: a WHERE clause that is applied to spatial data in order to specify which features will be displayed in a layer.
layer entry: a SAS catalog entry of type GISLAYER that includes the type of the layer (point, line, or area), as well as a layer definition and information about the graphical characteristics of the layer, such as the line color, the point symbol, or the fill pattern. See also layer definition.
line: in topological terms, a one-dimensional feature that is defined by two zero-dimensional features (points). A line starts at a designated point (the from-node) and ends at a designated point (the to-node), but it can also have intermediate (detail) points. Lines can represent streets, rivers, or boundaries. A line can also be referred to as a chain. See also from-node and to-node.
map: a graphic representation of an area. The area is often a geographic area, but it can also be any other area of any size.
map area: a polygon or group of polygons on a map. For example, states, provinces, and countries are typical map areas. In a map data set, a map area consists of all the observations that have the same values for the identification variable or variables. A map area is sometimes referred to as a unit area.
map data set: a SAS data set that contains information that the GMAP procedure uses to draw a map. Each observation in the data set contains variables whose values are the x, y coordinates of a point on the boundary of a map area. In addition, each observation contains an identification variable whose value identifies the map area that the point belongs to.
map entry: a SAS catalog entry of type GISMAP that contains the layers, links to key variables, the name of the label data set, the name of the coverage entry, legend information, and so on for a map.
Map window: the SAS/GIS window that displays the current map. The Map window enables you to interactively query attribute data and to modify the map.
MapInfo: a GIS software application that is developed and supported by MapInfo Corporation.
node: a point on a map that has connections to one or more chains. See also chain and point.
perimeter: the total length of the sides of a closed polygon. The perimeter value is calculated by the GIS procedure when the AREA option is used. See also area.
point: in topological terms, a zero-dimensional feature that is the base component upon which higher dimensional objects (lines and polygons) are defined. A point can represent a feature such as a house, a store, or a town. See also detail point.
polygon: a closed geometric figure that is bounded by lines or arcs. A polygon can be filled to represent a surface.
SAS catalog: a SAS file that stores many different kinds of information in smaller units called catalog entries. A single SAS catalog can contain several different types of catalog entries.
SAS data set: a file whose contents are in one of the native SAS file formats. There are two types of SAS data sets: SAS data files and SAS data views. SAS data files contain data values in addition to descriptor information that is associated with the data. SAS data views contain only the descriptor information plus other information that is required for retrieving data values from other SAS data sets or from files that are stored in other software vendors' file formats.
SAS library: a collection of one or more files that are recognized by SAS and that are referenced and stored as a unit. Each file is a member of the library.
SAS/GIS software: a SAS software product that provides an interactive windowing environment for analyzing and displaying data in a spatial or geographic context.
SAS/GRAPH software: a SAS software product that analyzes data and that visually represents the relationships between data values as two- and three-dimensional graphs.
shapefile: a format for spatial data files developed by ESRI.
spatial analysis: the process of analyzing data that can be referenced spatially in order to extract or generate new geographical information.
spatial data: coordinates and other information that are used for drawing maps. The maps can include features such as city boundaries, census tract boundaries, streets, schools, and so on. Spatial data is stored in three SAS data sets: the chains, nodes, and details data sets. See also attribute data.
spatial database: a database that contains the following three SAS/GIS data sets: chains, nodes, and details. A spatial database also contains catalog entries that define the information that is needed in order to display a map.
static layer: a layer in which the values of the graphical characteristics (fill color, outline color, line width, and so on) are the same for all features in the layer. See also layer and thematic layer.
thematic layer: a layer in which the graphical characteristics for each feature in the layer are determined by the values of response variables in an associated attribute data set. For example, line widths on a highway layer can represent traffic volumes, and fill colors on an area layer can represent population densities. See also layer and static layer.
TIGER: Topologically Integrated Geographic Encoding and Referencing. A format for map data that was developed by the United States Census Bureau. As of March 2008, the TIGER file format has been superceded by the TIGER shapefile format. See also shapefile.
to-node: the ending coordinates of a line segment on a SAS/GIS map. See also detail point, from-node, node, and point.
tool palette: in the GIS Map window, the collection of icons that represent functions in the interface.
variable: a column in a SAS data set or in a SAS data view. The data values for each variable describe a single characteristic for all observations. Each SAS variable can have the following attributes: name, data type (character or numeric), length, format, informat, and label.

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