Shapefile
| Shapefile | |
|---|---|
| File extension : |
.shp
|
| Developed by: | ESRI |
| Container for: | Geospatial data |
The file format Shapefile (often called Shapedaten or Shape ) is a format for vector spatial data originally developed for the ArcView software from ESRI .
development
The Shapefile is widespread as a quasi-standard in the desktop GIS environment because it is a fairly simple format and not very demanding in terms of data quality . Still, it is the format in which the most map data is available. The support of free as well as commercial programs and program libraries (e.g. GeoTools and Deegree ) is not as good with any format as with the Shapefiles. Many open source programs convert data from shapefiles to SQL for spatial databases.
construction
A shapefile is not a single file, it consists of at least three files:
- .shp is used to save the geometry data
- .dbf factual data in dBASE format
- .shx is used as an index of the geometry to link the factual data (also called attribute data)
Optional files
- .atx attribute index
- .sbx and .sbn spatial index
- .qix alternative spatial index ( used and created by GDAL )
- .aih and .ain index for table links (links)
- .shp.xml metadata about the shapefile
- .prj projection of the data
- .cpg to specify the character set used in the .dbf .
A shapefile can only contain elements of one type, e.g. B.
- Points,
- Lines,
- Areas (polygons)
- or multi-points
In addition to the respective type, the shapefile can always contain so-called null shapes. These have no geometry, but just like any other type they have a data record in the associated DBF file. Furthermore, a distinction can be made between 2D geometries and 3D geometries.
Optionally, the created design of a shapefile (line thickness, point symbols, colors, etc.) can be saved in a legend file (up to ArcView 3.3 * .avl, from ArcGIS-ArcView 8 * .lyr), as this information is not saved within a shapefile. The legend file can be added in the theme properties after loading a shapefile.
Format restrictions
- The size of the Shp and DBF files must not exceed 2 gigabytes.
The attribute database format for the DBF component file is based on an earlier dBase standard. This is accompanied by the following restrictions:
- While the current dBase format as well as GDAL / OGR (as an open source software library for reading and writing shapefiles) distinguishes empty fields as zero values from the number 0, ESRI Software does not make this distinction.
- limited support for Unicode field names
- Maximum length of the field names: 10 characters
- Maximum number of fields: 255
- Permitted field types are floating point (13 characters), whole number / integer, date without time storage (8 characters) and text (254 characters)
- Floating point numbers can contain rounding errors because they are stored as text
Web links
- ESRI Shapefile Technical Description (English, PDF; 127 kB) Detailed description of the ESRI Shapefiles (shp, shx and dbf)
- Shapelib C library for processing shapefiles
- geotools Java library for processing shapefiles and creating GIS applications
- OGR Simple Feature Library A C ++ open source library that provides read and write access to various vector file formats including ESRI shapefiles
- QGIS Free Open Source Geographic Information System (Shapefiles can be opened as vector layers)
- Shapefile Projection Finder - GIS tool for automatic detection of the unknown projection of a shapefile
Individual evidence
- ↑ ESRI HowTo: Read and write shapefile and dBASE file encoded in various code pages
- ↑ ArcGIS Desktop 9.3 Help - Geoprocessing considerations for shapefile output . Esri. April 24, 2009. Retrieved March 24, 2014.