ESRI シェープファイル
目次
ESRI シェープファイル
QGISで使う標準的なベクトルファイル形式はESRI Shapefileです。ShapefileはOGRの Simple Feature Library( http://www.gdal.org/ogr/ ) の機能を利用してサポートされてます。実際にはshapefileはいくつかのファイルで構成されています。以下の3種類のファイルは必須で必要です:
- .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 . .
Shapefileのロード
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.
Tip 8
When you add a layer to the map, it is assigned a random color. When adding more than one layer at a time, different colors are assigned to each layer.
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 5.4.2 for more information on setting symbology of vector layers.
パフォーマンスの改善
To improve the performance of drawing a shapefile, you can create a spatial index. 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.
MapInfo Layerのロード
To load a MapInfo layer, click on the Add 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.
ArcInfo Binary Coverageのロード
To load an ArcInfo binary coverage click on the Add a vector layer toolbar button or type V to open the Add Vector Layer dialog. Select Directory. Change to Type Arc/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.