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SDViewer -- Map Layer Operations: Creating New Shapefiles Map Layer Operations are features that enable extracting and manipulating shapefile and TIGER/Line files that have been added to the project. These tools may be used to create, for example, a shapefile that includes only designated school districts in a region. Resulting shapefiles may then be used as additional map layers in a project. As an example, you might want to add a "bolded red outline" showing only those districts of specific analytical interest. This feature may be used with any type of shapefile. Map Layer Operations may also be used to convert selected features of TIGER/Line files to shapefiles. These tools may be used to create, for example, a shapefile that includes only boundaries of census tracts in a region -- roads/streets of a certain type, like Interstate highways. Resulting shapefiles may then be used as additional map layers in a project. As an example, you might want to add only Interstate highways for a specific area to project. This feature may be used to extract any type of Census Feature Class Code (CFCC) and other field attributes of TIGER/Line files. This section shows examples of the use of the Map Layer Operations to perform these tasks. The Map Layer Operations are invoked via the File>ManageLayers menu. 
Extracting Selected Districts to New Shapefile.
In this example, the export layer feature is used to select unified school districts in Texas
(state FIPS code 48) which have 2002-03 enrollment of 25,000 or more.
The layer "sdu" (referenced in the project by this shorthand name) is used as the source file.
The query stdist like '48%' and e2002>25000 is used as the criteria to select polygons (in this case) to be extracted and included in a new shapefile. The STDIST field contains the state FIPS code and the school district Federal ID code. the SQL query "like" is used and the field values are wildcarded with the % reference -- it will take any unified school district in the state based on this part of the query. The field e2002 contains the 2002-03 enrollment. After the export layer operation, the saved shapefile is then added to the project and displayed. The districts are shown in red in the graphic presented below. 
Extracting Selected Line Segments from a TIGER/Line File. In this example, the export layer feature is used to select line segments in the Bexar County, Texas TIGER/Line (TLF) file that are in census tract 1613.01 and create a new shapefile containing line segments only in this census tract. The Bexar County TLF is auto-downloaded and add to the project using the GetWebGeodata feature. The name assigned is TGR48209 (standard TLF naming convention). The export layer query statement tractl='161301' and tractr='161301' is used as shown in the next view. This query statement says to extract all line segments that are coded with census tract 161301 (1613.01) on the right or left side of the line segment. 
The resulting shapefile generated has been added to the project and the line segment coded as red. This shapefile can now be used by any software that can read a shapefile and used in whatever application may be of interest. |
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