「ESRI シェープファイル」の版間の差分

2009年9月5日 (土) 21:03時点における版

ESRI Shapefiles

The standard vector file format used in QGIS is the ESRI Shapefile. Support is provided by the OGR Simple Feature Library( http://www.gdal.org/ogr/ ). A shapefile actually consists of several files. The following three are required: <P>

• .shp file containing the feature geometries.
• .dbf file containing the attributes in dBase format.
• .shx index file.

<P> Shapefiles also can include a file with a .prj suffix, which contains the projection information. While it is very useful to have a projection file, it is not mandatory. A shapefile dataset can contain additional files. For further details see the ESRI technical specification at http://www.esri.com/library/whitepapers/pdfs/shapefile.pdf . .

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Loading a Shapefile

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<P> [width=0.7cm]mActionAddNonDbLayer To load a shapefile, start QGIS and click on the mActionAddNonDbLayerAdd a vector layer toolbar button<A NAME="58"></A> or simply type V. This will bring up a new window (see Figure<A HREF="#fig:addvectorlayer">5</A>).

<P> From the available options check File. Click on Browse. That will bring up a standard open file dialog (see Figure <A HREF="#fig:openshapefile">6</A>) which allows you to navigate the file system and load a shapefile or other supported data source. The selection box Files of type... allows you to preselect some OGR supported file formats.

<P> You can also select the Encoding type for the shapefile if desired.

<P> Selecting a shapefile from the list and clicking Open loads it into QGIS. Figure <A HREF="#fig:loadedshapefile">7</A> shows QGIS after loading the alaska.shp file.

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<P> Once loaded, you can zoom around the shapefile using the map navigation tools. To change the symbology of a layer, open the Layer Properties dialog by double clicking on the layer name or by right-clicking on the name in the legend and choosing Properties from the popup menu. See Section <A HREF="node17.html#sec:symbology">5.4.2</A> for more information on setting symbology of vector layers.

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Improving Performance

<P> To improve the performance of drawing a shapefile, you can create a spatial index. A <A NAME="81"></A> spatial index will improve the speed of both zooming and panning. Spatial indexes used by QGIS have a .qix extension.

<P> Use these steps to create the index:

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• Load a shapefile.
• Open the Layer Properties dialog by double-clicking on the shapefile name in the legend or by right-clicking and choosing Properties from the popup menu.
• In the tab General click the Create Spatial Index button.

Loading a MapInfo Layer

<P> To load a MapInfo layer, click on the mActionAddNonDbLayerAdd a vector layer toolbar bar button or type V, change the file type filter to Files of Type[OGR] MapInfo (*.mif *.tab *.MIF *.TAB) and select the layer you want to load.

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Loading an ArcInfo Binary Coverage

<P> To load an ArcInfo binary coverage click on the mActionAddNonDbLayerAdd a vector layer toolbar button or type V to open the Add Vector Layer dialog. Select Directory. Change to TypeArc/Ingo Binary Coverage. Navigate to the directory that contains the coverage files and select it.

<P> Similarly, you can load directory based vector files in the UK National Transfer Format as well as the raw TIGER Format of the US Census Bureau.

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