Editing GIS file format (section)

==Vector formats{{Anchor|Vector}}==
{{further|Vector graphics|Data model (GIS)#Vector data model}}

[[Image:Simple vector map.svg|thumb|250px|right|A simple vector map, using each of the vector elements: points for wells, lines for rivers, and a polygon for the lake]]
A ''vector'' dataset (sometimes called a ''feature'' dataset) stores information about discrete objects, using an encoding of the [[Vector graphics|vector logical data model]] to represent the location or ''geometry'' of each object, and an encoding of its other properties that is usually based on [[relational database]] technology. Typically, a single dataset collects information about a set of closely related or similar objects, such as all of the roads in a city.

The Vector data model uses [[coordinate geometry]] to represent each shape as one of several [[geometric primitive]]s, most commonly ''[[Point (geometry)|points]]'' (a single coordinate of zero [[dimension]]), ''[[Line (geometry)|lines]]'' (a one-dimensional ordered list of coordinates connected by straight lines), and ''[[polygon]]s'' (a self-closing boundary line enclosing a two-dimensional region). Many data structures have been developed to encode these primitives as digital data, but most modern vector file formats are based on the [[Open Geospatial Consortium]] (OGC) [[Simple Features]] specification, often directly incorporating its [[Well-known text representation of geometry|Well-known text]] (WKT) or Well-known binary (WKB) encodings.

In addition to the geometry of each object, a vector dataset must also be able to store its ''attributes''. For example, a database that describes lakes may contain each lake's depth, water quality, and pollution level. Since the 1970s, almost all vector file formats have adopted the [[relational database]] model, either in principle or directly incorporating [[relational database management system|RDBMS]] software. Thus, the entire dataset is stored in a ''table'', with each ''row'' representing a single object that contains ''columns'' for each attribute.<ref name="longley2011" />{{rp|256}}

Two strategies have been used to integrate the geometry and attributes into a single vector file format structure:<ref name="chang2014">{{cite book |last1=Chang |first1=Kang-tsung |title=Introduction to Geographic Information Systems |date=2014 |publisher=McGraw-Hill |isbn=978-0-07-352290-6 |pages=50–57 |edition=7th}}</ref>
* A ''[[Georelational data model|georelational format]]'' stores them as two separate files, with the geometry and attributes of each object being linked by file ordering or a [[primary key]]. This was most common from the 1970s through the early 1990s, because GIS software developers had to invent their own geometry data structures, but incorporated existing relational database file formats  for the attributes. For example, the [[Esri]] [[Shapefile]] format includes the .dbf file from the DOS [[dBase]] software.
* The ''Object-based model'' stores them in a single structure, loosely or directly based on the objects in [[object-oriented programming]] languages. This is the basis of most modern file formats, including [[spatial database]]s that include a geometry column along with the other attributes in a single relational table. Other formats, such as [[GeoJSON]], use different structures for geometry and attributes, but combine them for each object in the same file.

[[Geospatial topology]] is often an important part of vector data, representing the inherent spatial relationships (especially adjacency) between objects. Topology has been managed in vector file formats in four ways. In a ''topological data structure'', most notably Harvard's POLYVRT and its successor the [[ArcInfo|ARC/INFO]] coverage, topological connections between points, lines, and polygons are an inherent part of the encoding of those features.<ref name="bolstad" />{{rp|46–49}} Conversely, non-topological or ''spaghetti data'' (such as the Esri [[Shapefile]] and most [[spatial database]]s) includes no topology information, with each geometry being completely independent of all others. A ''topology dataset'' (often used in [[Transport network analysis|network analysis]]) augments spaghetti data with a separate file encoding the topological connections.<ref name="longley2011">{{cite book |last1=Longley |first1=Paul A. |last2=Goodchild |first2=Michael F. |last3=Maguire |first3=David J. |last4=Rhind |first4=David W. |title=Geographic Information Systems & Science |date=2011 |publisher=Wiley |edition=3rd}}</ref>{{rp|218}} A ''topology rulebase'' is a list of desired topology rules used to enforce spatial integrity in spaghetti data, such as "county polygons must not overlap" and "state polygons must share boundaries with county polygons."<ref name="chang2014" />

Vector datasets usually represent discrete [[geographical feature]]s, such as buildings, trees, and counties. However, they may also be used to represent [[Field (geography)|geographical fields]] by storing locations where the spatially continuous field has been sampled. Sample points (e.g., [[weather stations]] and [[sensor networks]]), [[Contour line]]s and [[triangulated irregular network]]s (TIN) are used to represent elevation or other values that change continuously over space. TINs record values at point locations, which are connected by lines to form an irregular mesh of triangles. The face of the triangles represent the terrain surface.

===Example vector file formats===
{{see also|Comparison of GIS vector file formats}}
Formats commonly in current usage:
*[[Shapefile]] – a popular vector data GIS format, developed by [[Esri]]
*[[Geography Markup Language]] (GML) – XML based open standard (by [[OpenGIS]]) for GIS data exchange
*[[GeoJSON]] – a lightweight format based on [[JSON]], used by many open source GIS packages
*[[GeoMedia]] – [[Intergraph]]'s [[Microsoft Access]] based format for spatial vector storage
*[[Keyhole Markup Language]] (KML) – XML based open standard (by [[OpenGIS]]) for GIS data exchange
*[[MapInfo TAB format]] – [[MapInfo Corporation|MapInfo]]'s vector data format using TAB, DAT, ID and MAP files
*[[Measure Map Pro format]] – [[XML]] data format to store GIS data
*[[National Transfer Format]] (NTF) – National Transfer Format (mostly used by the UK Ordnance Survey)
*[[Spatialite]] – a spatial extension to [[SQLite]], providing vector geodatabase functionality. It is similar to [[PostGIS]], [[Oracle Spatial]], and SQL Server with spatial extensions
*[[Simple Features]] – [[Open Geospatial Consortium]] specification for vector data
**[[Well-known text representation of geometry|Well-known text]] (WKT) – A text markup language for representing feature geometry, developed by [[Open Geospatial Consortium]]
**[[Well-known text representation of geometry|Well-known binary]] (WKB) – Binary version of well-known text, used in many [[spatial database]]s
*[[SOSI]] – a spatial data format used for all public exchange of spatial data in Norway
* [[AutoCAD DXF]] – data transfer format for [[AutoCAD]] data (by [[Autodesk]])
*[[Geographic Data Files]] (GDF) — An interchange file format for geographic data

Historical formats seldom used today:
*[[ArcInfo]] Coverage - topological data structure used in Arc/INFO from 1981 through 2000
*[[Esri TIN]] – proprietary [[binary data|binary]] format for [[triangulated irregular network]] data used by [[Esri]]
*[[Digital line graph]] (DLG) – a USGS format for vector data
*[[TIGER]] – Topologically Integrated Geographic Encoding and Referencing
*[[Vector Product Format]] (VPF) – [[National Geospatial-Intelligence Agency]] (NGA)'s format of vectored data for large geographic databases
* [[Spatial Data File]] – [[Autodesk]]'s high-performance geodatabase format, native to [[MapGuide]]
* ISFC – [[Intergraph]]'s [[MicroStation]] based CAD solution attaching vector elements to a relational [[Microsoft Access]] database
*[[Dual Independent Map Encoding]] (DIME) – A historic GIS file format, developed in the 1960s