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18-487: In addition, NHGIS has created historical and contemporary cartographic boundary shapefiles compatible with every census, and over 50 million lines of metadata describing the collection. Historical U.S. state and county boundaries are available 1790–present, with smaller geographies available as the U.S. Census Bureau created them. Census Tract boundaries are available 1910–present and Block Group and Block boundaries available 1990–present. The cartographic boundary files and

36-799: A small company which offers both free and professional licenses. This article relating to the history of the United States is a stub . You can help Misplaced Pages by expanding it . Shapefile The shapefile format is a geospatial vector data format for geographic information system (GIS) software . It is developed and regulated by Esri as a mostly open specification for data interoperability among Esri and other GIS software products . The shapefile format can spatially describe vector features: points , lines , and polygons , representing, for example, water wells , rivers , and lakes . Each item usually has attributes that describe it, such as name or temperature . The shapefile format

54-405: Is a digital vector storage format for storing geographic location and associated attribute information. This format lacks the capacity to store topological information. The shapefile format was introduced with ArcView GIS version 2 in the early 1990s. It is now possible to read and write geographical datasets using the shapefile format with a wide variety of software. The shapefile format stores

72-457: Is not documented by Esri. However it has been reverse-engineered and documented by the open source community. The 100-byte header is similar to the one in .shp . It is not currently implemented by other vendors. The .sbn file is not strictly necessary, since the .shp file contains all of the information necessary to successfully parse the spatial data. The shapefile format has a number of limitations. The shapefile format does not have

90-556: Is prefixed with a record header of 8 bytes: Following the record header is the actual record: The variable-length record contents depend on the shape type, which must be either the shape type given in the file header or Null. The following are the possible shape types: Optional : M Optional : M range, M array Optional : M range, M array Optional : M range, M array Optional : M range, M array Optional : M range, M array Optional Fields : M range, M array Optional : M range, M array The index contains positional index of

108-405: Is public knowledge, and has been implemented in many dBase clones known as xBase . The open-source shapefile C library, for example, calls its format "xBase" even though it's plain dBase IV. The names and values of attributes are not standardized, and will be different depending on the source of the shapefile. This is a binary spatial index file, which is used only by Esri software. The format

126-478: The .dbf component file is based on an older dBase standard. This database format inherently has a number of limitations: Because the shape type precedes each geometry record, a shapefile is technically capable of storing a mixture of different shape types. However, the specification states, "All the non-Null shapes in a shapefile are required to be of the same shape type." Therefore, this ability to mix shape types must be limited to interspersing null shapes with

144-563: The .shp file, but alone is incomplete for distribution as the other supporting files are required. In line with the ESRI Shapefile Technical Description , legacy GIS software may expect that the filename prefix be limited to eight characters to conform to the DOS 8.3 filename convention, though modern software applications accept files with longer names. In each of the .shp , .shx , and .dbf files,

162-511: The AutoCAD shape font source format, which shares the .shp extension. The 2D axis ordering of coordinate data assumes a Cartesian coordinate system , using the order (X Y) or (Easting Northing). This axis order is consistent for Geographic coordinate systems , where the order is similarly (longitude latitude). Geometries may also support 3- or 4- dimensional Z and M coordinates, for elevation and measure, respectively. A Z-dimension stores

180-439: The ability to store topological relationships between shapes. The ESRI ArcInfo coverages and many geodatabases do have the ability to store feature topology. The size of both .shp and .dbf component files cannot exceed 2 GB (or 2 bytes) — around 70 million point features at best. The maximum number of feature for other geometry types varies depending on the number of vertices used. The attribute database format for

198-420: The correct position in the .shp file. It is also possible to seek forwards an arbitrary number of records using the same method. It is possible to generate the complete index file given a lone .shp file. However, since a shapefile is supposed to always contain an index, doing so counts as repairing a corrupt file. This file stores the attributes for each shape; it uses the dBase IV format. The format

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216-586: The elevation of each coordinate in 3D space , which can be used for analysis or for visualisation of geometries using 3D computer graphics . The user-defined M dimension can be used for one of many functions, such as storing linear referencing measures or relative time of a feature in 4D space . The main file header is fixed at 100 bytes in length and contains 17 fields; nine 4-byte (32-bit signed integer or int32) integer fields followed by eight 8-byte ( double ) signed floating point fields: The file then contains any number of variable-length records. Each record

234-409: The feature geometry and the same 100-byte header as the .shp file, followed by any number of 8-byte fixed-length records which consist of the following two fields: Using this index, it is possible to seek backwards in the shapefile by, first, seeking backwards in the shape index (which is possible because it uses fixed-length records), then reading the record offset, and using that offset to seek to

252-489: The geometry as primitive geometric shapes like points, lines, and polygons. These shapes, together with data attributes that are linked to each shape, create the representation of the geographic data. The term "shapefile" is quite common, but the format consists of a collection of files with a common filename prefix, stored in the same directory . The three mandatory files have filename extensions .shp , .shx , and .dbf . The actual shapefile relates specifically to

270-445: The geometry data. Geometry of a given feature is stored as a set of vector coordinates. The binary file consists of a single fixed-length header followed by one or more variable-length records . Each of the variable-length records includes a record-header component and a record-contents component. A detailed description of the file format is given in the ESRI Shapefile Technical Description . This format should not be confused with

288-419: The shapes in each file correspond to each other in sequence (i.e., the first record in the .shp file corresponds to the first record in the .shx and .dbf files, etc.). The .shp and .shx files have various fields with different endianness , so an implementer of the file formats must be very careful to respect the endianness of each field and treat it properly. The main file ( .shp ) contains

306-442: The single shape type declared in the file's header. A shapefile must not contain both polyline and polygon data, for example, the descriptions for a well (point), a river (polyline), and a lake (polygon) would be stored in three separate datasets. Header (computing) In information technology , header refers to supplemental data placed at the beginning of a block of data being stored or transmitted. In data transmission ,

324-847: The tabular data are formatted so as to be easily linked for use in Geographic Information System software. NHGIS was launched in 2007 and is maintained by the Minnesota Population Center at the University of Minnesota and is funded by the National Science Foundation and the National Institutes of Health . Much of the historical data are viewable as tables or interactive maps in Social Explorer,

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