ESRI シェープファイル
目次
ESRI シェープファイル
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:
- .shp file containing the feature geometries.
- .dbf file containing the attributes in dBase format.
- .shx index file.
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 . .
Loading a Shapefile
To load a shapefile, start QGIS and click on the Add a vector layer toolbar button or simply type V. This will bring up a new window (see Figure5).
From the available options check File. Click on Browse. That will bring up a standard open file dialog (see Figure 6) 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.
図 5: Add Vector Layer Dialog |
You can also select the Encoding type for the shapefile if desired.
Selecting a shapefile from the list and clicking Open loads it into QGIS. Figure 7 shows QGIS after loading the alaska.shp file.
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.
Improving Performance
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.
Use these steps to create the index:
- 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.
図 6: Open an OGR Supported Vector Layer Dialog |
- In the tab General click the Create Spatial Index button.
Loading a MapInfo Layer
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.
Loading an ArcInfo Binary Coverage
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.
図 7: QGIS with Shapefile of Alaska loaded |
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.