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Data Set and Catalog Entry Interactions

SAS/GIS software uses SAS catalog entries to store metadata for the spatial database-that is, information about the spatial data values in the spatial data sets. SAS/GIS spatial databases use the following entry types.

Spatial Entries

A spatial entry is a SAS catalog entry of type GISSPA that identifies the spatial data sets for a given spatial database and defines relationships between the variables in those data sets.

SAS/GIS software supports simple spatial entries and compound spatial entries as follows:

Simple spatial entries contain:

• references to the chains, nodes, and details data sets that contain spatial information.

• references to any polygonal index data sets that define the boundaries of area features in the spatial data.

• definitions for composite associations that specify how the variables in the spatial data sets are used. See Composites for more information on composite associations.

• the definition for a lattice hierarchy that specifies which area features in the spatial data enclose or are enclosed by other features.

• the parameters for the projection system used to interpret the spatial information stored in the spatial data sets.

• the bounding extents of the spatial data coordinates, consisting of the minimum and maximum X and Y coordinate values and the ranges of X and Y values.

Merged spatial entries

contain logical references to two or more other child spatial entries, along with a specification of how the entries were merged (by overlapping or edge matching). A merged spatial database consists of multiple SAS/GIS spatial databases linked together hierarchically in a tree structure.

For example, if you have two spatial databases, each containing the county boundaries for one of a pair of neighboring states, you could build a merged spatial that contains both states and view the two maps together. You don't need to import another map containing the two states; the merged spatial points to the two "child" spatial entries.

Spatial entries are created and modified using the SPATIAL statement in the GIS procedure.

Note:   You can also create a new spatial entry by making the following selections from the GIS Map Window's menu bar:

[File][Save As][Spatial]   

The following additional statements in the GIS procedure also update the information in the spatial entry:

COMPOSITE statement

creates or modifies composites that define the relation and function of variables in the spatial data sets. The composite definition is stored in the spatial entry. See The GIS Procedure and the section in SAS/GIS Software: Usage and Reference, Version 6 about COMPOSITE statements for details on using the GIS procedure to create or modify composites.

POLYGONAL INDEX statement

updates the list of available index names stored in the spatial entry. See The GIS Procedure and the section in SAS/GIS Software: Usage and Reference, Version 6 about POLYGONAL INDEX statements for details of using the GIS procedure to create or modify polygonal indexes.

LATTICE statement

updates the lattice hierarchy stored in the spatial entry. See The GIS Procedure and the section in SAS/GIS Software: Usage and Reference, Version 6 about LATTICE statements for details of the using the GIS procedure to define lattice hierarchies.

You can view a formatted report of the contents of a spatial entry by submitting a SPATIAL CONTENTS statement in the GIS procedure.

See The GIS Procedure and the section in SAS/GIS Software: Usage and Reference, Version 6 about SPATIAL statements for more information about using the GIS procedure to create, modify, or view the contents of spatial entries.

Coverage Entries

A coverage entry is a SAS catalog entry of type GISCOVER that defines the subset, or coverage, of the spatial data that is available to a map. SAS/GIS maps refer to coverages rather than directly to the spatial data.

A coverage entry contains the following elements:

• a reference to the root spatial entry.

• a WHERE clause that describes the logical subset of the spatial data that is available for display in a map.

  Note:   The clause WHERE='1' can be used to define a coverage that includes all the data in the spatial database. WHERE='1' is called a Universal Coverage.   

  The WHERE clause binds the coverage entry to the spatial data sets that it subsets. The WHERE clause is checked for compatibility with the spatial data when the coverage entry is created and also whenever a map that uses the coverage entry is opened.

• the maximum and minimum X and Y coordinates in the portion of the spatial data that meets the WHERE clause criteria for the coverage.

  These maximum and minimum coordinates are evaluated when the coverage is created. The GIS procedure's COVERAGE CREATE statement reads the matching chains and determines the extents from the chains; XMIN, YMIN, XMAX, and YMAX variables. If you make changes to the chains, nodes, and details data sets that affect the coverage extents, you should use the COVERAGE UPDATE statement to update the bounding extent values.

Multiple coverage entries can refer to the same spatial entry to create different subsets of the spatial data for different maps. For example, you could define a series of coverages to subset a county into multiple sales regions according to the block groups contained in each of the regions. The spatial data for the entire county would still be in a single spatial database represented by the chains, nodes, and details data sets and the controlling spatial entry.

Coverage entries are created and modified using the COVERAGE statement in the GIS procedure. You can view a formatted report of the contents of a coverage entry by submitting a COVERAGE CONTENTS statement in the GIS procedure. (The contents report for a coverage entry will also include all the contents information for the root spatial entry as well.)

See The GIS Procedure for more information about using the GIS procedure to create, modify, or view the contents of coverage entries.

Layer Entries

A layer entry is a SAS catalog entry of type GISLAYER that defines the set of features that comprise a layer in the map. A layer entry contains the following elements:

• a WHERE clause that describes the common characteristic of features in the layer.

  The WHERE clause binds the layer entry to the spatial data even though it is stored in a separate entry. The layer is not bound to a specific spatial entry, just to those entries representing the same type of data. Therefore a layer created for use with data imported from a TIGER file can be used with data imported from any TIGER file; however, not all filetypes can take advantage of this behavior. The WHERE clause is checked for compatibility with spatial data when the layer entry is created and also whenever a map that uses the layer entry is opened.

  Note:   When defining area layers, you can specify a composite as an alternative to specifying an explicit WHERE clause. However, the layer entry stores the WHERE clause implied by the composite. For example, if you specify STATE as the defining composite for a layer, and the STATE composite specifies the following variables: VAR=(LEFT=STATEL,RIGHT=STATER), then the implied WHERE clause stored in the layer entry is 'STATEL NE STATER'.   

• option settings for the layer such as the layer type (point, line, or area), whether the layer is static or thematic, whether it is initially displayed or hidden, whether detail points are drawn for the layer, and the scales at which the layer is automatically turned on or off.

• the graphical attributes necessary to draw the layer when it is displayed as a static layer.

• The attribute links, theme range breaks, and graphical attributes if the layer contains themes.

Map Entries

A map entry is a SAS catalog entry of type GISMAP. Map entries are the controlling entries for SAS/GIS maps because they tie together all the information needed to display a map. A map entry contains the following elements:

• a reference to the coverage entry that defines the subset of the spatial data that is available to the map. Note that the map entry refers to a particular coverage of the spatial data rather than directly to the spatial entry.

• references to the layer entries for all layers included in the map.

• references to any attribute data sets associated with the map, for example, the data sets used for the map actions, along with definitions of how the attribute data sets are linked to the spatial data.

• a reference to the SAS data set that contains labels for map features.

• definitions for the actions that can be performed.

• definitions for map legends.

• parameters for the projection system used to project spatial data coordinates for display.

• option settings for the map, including the following:
  • the units and mode for the map scale

  • whether coordinate, distance, and attribute feedback are displayed

  • whether detail points are read

  • whether the tool palette is active.

Map entries are created using the MAP CREATE statement in the GIS procedure. However, much of the information stored in the map entry is specified interactively in the GIS Map window.

You can view a formatted report of the contents of a map entry by submitting a MAP CONTENTS statement in the GIS procedure. (The contents report for a map entry includes all the contents information for the spatial, coverage, and layer entries as well.)

See The GIS Procedure for details of the items that can be specified with the GIS procedure and the section on SAS/GIS Windows for details of the items that can be specified interactively in the GIS Map window.

Composites

For most operations involving the spatial database, you refer to composites of the spatial data variables rather than directly to the variables in the spatial data sets. A composite consists of the following elements:

• a variable association that identifies which variable or variables in the spatial database comprise the association. The variable association can specify a single variable, a pair of variables that define a bilateral (left-right) association, or two pairs of variables that define the start and end of a directional (from-to) bilateral association.

• a class attribute that identifies the role of the composite in the spatial database.

For example, if the chains data set has a variable named FEANAME that contains feature names, you can create a composite for the FEANAME variable that assigns the class attribute NAME to indicate that the association represents feature names. Or, if the chains data set has COUNTYL and COUNTYR variables that contain the codes for the counties on the left and right sides of the chains, you can create a composite named COUNTY that identifies the bilateral relationship between these two variables and assigns the class attribute AREA to indicate that the association defines county areas in the spatial data.

Composites are created and modified using the COMPOSITE statement in the GIS procedure. composite definitions are stored in the spatial entry.

See The GIS Procedure for more information about using the GIS procedure to create or modify composites.

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