Vector data models structures vector data models can be structured many different ways. This slide gives a graphic example of how the vector data structure is stored using the spaghetti data structure. The spatial resolution of a raster dataset represents a measure of the accuracy or detail of the displayed information. In particular, the quadtree data structure has found some. What are raster and vector data in the gis context.
Raster gis databases are arrangements of grid cells or pixels that are referenced by row and column positions. A raster representation for scalable image and volume data. Idrisi and other software is based on the vector spatial data model e. The advantages and disadvantages of vector and raster data. The raster data model is widely used by nongis technologies such as digital cameraspictures and lcd monitors. In rastor, the area under consideration is divided into equal squares and a characteristic assigned to it. Topological connections may be quite important when rasters are.
A raster representation for scalable image and volume data joe kniss, warren hunt, kristin potter, pradeep sen abstract topology has been an important tool for analyzing scalar data and. There are many analysis that make use of both data models i. Dual independent map encoding dime format o developed by us bureau of the census o nodes intersections of lines are identified with codes o assigns a directional code in the form of a from node and a to node. Coding best works when neighboring pixels are similar 2. Raster is a method for the storage, processing and display of spatial data. For effective analysis, vector data must be converted into a topological structure. Raster and vector refer to a particular data model a data structure refers to a particular implementation of either the raster or vector model 4 topology the spatial relationships between things an important distinction between data models and data structures can be stored or calculated on the fly 5 raster vector data models numerous differences in terms of. Raster data sets are characterised by their grid cell structure, whereas the vector approach comprises coordinate geometry in an attempt to represent the features or objects of. A simple data structurea matrix of cells with values, representing a coordinate, and sometimes linked to an attribute table.
While the term raster implies a regularly spaced grid other tessellated data structures do exist in grid based gis systems. Spatial data types provide the information that a computer requires to reconstruct the spatial data in digital form. Pdf the raster data model is a widely used method of storing geographic data. Introduction to gis and spatial data vector and raster comparison vector raster compact data structure for homogenous areas. Although this may be heresy to many users, there are advantages to using shapefiles that violate planar assumptions i. These are vector data model and raster data models. Now a spatial data can be divided in 3 main categories. Each grid cell is filled with the measured attribute values. Different types of vector data and concept of topology nptel.
The gis spatial data model university of washington. Topology in raster and vector representation springerlink. Flexible no limits on the type of spatial data that can be stored, including geographic area, units of measure, data type raster and vector, coordinate reference systems, scale, and more. The data base concept is central to a gis and is the main difference between a. In an enterprise geodatabase, raster data is stored in a structure where the data is tiled, indexed, pyramided, and most often compressed. Notice along the shared boundary between the parcels, the coordinates for the boundary are stored redundantly. Divides space into discrete features, usually points, lines or polygons.
It uses topology spatial relationships to represent spatial objects in addition to the use of geometry coordinates thorough adjacency, containment. Which vector formats have been created by the government. Exploring data structures 2 geodatabases can have behaviors detailed within the data structure to better model realworld relationships. Because of tiling, indexing, and pyramiding, each time the raster data is queried, only the tiles necessary to satisfy the extent and resolution of the query are returned instead of the whole dataset. The topo to raster tool is an interpolation method specifically designed for the creation of hydrologically correct digital elevation models dems. Each area is divided into rows and columns, which form a regular grid structure. Can overlay displays easily can easily manipulate data table can have many variables linked to one geographic file better suited for map output a simple data structure. Raster data are derived from a gridbased system of contiguous cells containing specific attribute information.
Every house, every tree, every city has its own unique latitude and longitude coordinates. File geodatabase are more current and exhibit several advantages over personal. Spatial data models and structures semantic scholar. As resolution increases, the size of the cell decreases. But this comes at a cost for speed of processing and data storage. Vector representation of data in the vector based model, geospatial data is represented in the form of coordinates. Furthermore, topology is static, and any editing of the vector data requires rebuilding of the topology. Difficult to resolve fine details little to no variation of values of large area. The use of large cells to reduce data volumes structures can be lost and there can be a serious loss of information crude raster maps are considerably less beautiful than line maps. Advantages of vector data models over raster model answers. As well as employing the raster and vector spatial data models1 we. Topology is also used for analyzing spatial relationships in many situations, such as dissolving the boundaries between adjacent polygons with the same attribute values or traversing a network of the elements in a topology graph.
Vector data can have quality issues such as undershoots, overshoots and slivers which you need to be aware of. The simplest use of dynamic might be the case of dynamically generated maps, for example on a web site or a gpsbased navigation system. Deltamapgenamap tiled topological and coverage raster. Length encoding quad tree used when values change continuously cell. It becomes thus possible to determine the topological relation of two regions, given in raster representation, with the same reasoning as in vector representations. Raster data structure refers to the method or format for storing raster data so that it can be used efficiently. This contributes to the merging of raster and vector operations. Vector data utilizes points, lines, and polygons to represent the spatial features in a map. Deltamapgenamap tiled topological and coverage raster data. Vector representation vector representation of data in the vector based model figure 4, geospatial data is represented in the form of coordinates. While coverages use the standard arcnode topology data structure, in which adjacent polygons share common bounding arcs, shapefiles store each feature as a separate object.
Data analysis since most input data does not exist in a topological data structure, topology must be built with the gis software. Pdf topology in raster and vector representation researchgate. A point may be represented by a single cell, a line by a sequence of neighbouring cells and a polygon by a collection of contiguous cells. Egenhofers nineintersection, wellknown for vector representations, is defined here on a raster, using a hybrid raster model, and then systematically transformed to yield functions which can be used in a convolution operation applied to a regular raster representation.
Why do we have so many types of data formats, and why are they so difficult to use together. Vector data may or may not be topologically explicit, depending on the files data structure. Whats the difference between gis spatial data types. Each cell must be rectangular in shape, but not necessarily square. The details of all publications are in the researchgate in full text pdf forms. Raster datasets can become potentially very large because they record values for each cell in an image. Within the spatial referenced data group, the gis data can be further classified into two different types. Learn more about thematic and continuous data while the structure of raster data is simple, it is exceptionally useful for a wide range of applications. Spatial data can represent vector and raster data models realworld features that have discrete boundaries such as roads, buildings, lakes, rivers, administrative boundaries as well as realworld phenomenafeatures that have nondiscrete boundaries such as precipitation and nutrient levels, terrain. Introduction to gis basics, data, analysis case studies.
It provides a more compact data structure than the raster model. Applying functions, the hybrid raster elements need not be stored. Raster and vector are the two basic data structures for storing and. Nov 26, 2017 while deciding whether to use a vector data model or raster data model in your work it entirely depends on the data you have as input and what your goals are for displaying or analyzing the data. Depending on the data set this can be a cpu intensive and time consuming procedure.
While the structure of raster data is simple, it is exceptionally useful for a wide range of applications. Vector and raster data both have their advantages and disadvantages. Spatial concepts, geometric data models and data structures, in d. Does anyone have some small, concise, effective pictures which convey and contrast these two fundamental data representations. A raster is an array of cells, where each cell has a value representing a specific portion of an object or a feature. In general terms what applications, processes, or analysis are each suited for. It provides efficiently encoding of topology and as result more efficiently. There are two broad categories of spatial data models. A point may be represented by a single cell, a line by a sequence of neighbouring cells and a polygon by a collection of contiguous cells all cells in a raster must be the same size, determining the resolution. Jan 14, 2011 for effective analysis, vector data must be converted into a topological structure.
Raster data are good for showing continually varying information. What is the difference between vector and raster data. Data volume and redundancy dense grid of data involves large memory requirements and computer power. Each of these units is composed simply as a series of one or more coordinate points, for example, a line is a collection of related points, and a polygon is a collection of related lines. Also, topology among graphical objects or items are much easier to be. Attribute data the information linked to the geographic features spatial data describing them. Oct 01, 2016 data analysis since most input data does not exist in a topological data structure, topology must be built with the gis software. The size of pixels in a raster determines its spatial resolution. This building process involves the creation of the topological tables and the definition of the arc, node, and polygon entities. Simulation easy, because cells have the same size technology is cheap disadvantages of raster data structures. Raster data sets are characterised by their grid cell structure, whereas the vector approach comprises coordinate geometry in an attempt to represent the features or objects of interest as exactly as possible. In the raster world, we have grid cells representing real world features. Each of these units is composed simply as a series of one or more coordinate points, for example, a line is a collection of related points. The model most commonly takes the form of a gridlike structure that.
L155 gis data models and data processing lecture 3 dr. Flexible no limits on the type of spatial data that can be stored, including geographic area, units of measure, data type raster and vector, coordinate reference systems, scale. Its cell values are written into a file by row and column. Cellby cell encoding a raster model is stored as a matrix. In vector data, the basic units of spatial information are points, lines arcs and polygons. Raster is often background visualization for vector data courtesy of. A physical entity is represented by a spatial object in a gis. There are two types of geodatabases freely available to all arc users, personal geodatabases and file geodatabases. Real world objects can be divided into two abstractions. Learn vocabulary, terms, and more with flashcards, games, and other study tools. However, the distinction between vector and raster data types is not unique to gis. Raster data components cells, pixels, grid cell size, spatial resolution bands spatial reference examples of raster data remotely sensed imagery bv, dn dem elevation drg color raster data structure header dimension and spatial resolution projection and coordinates. While deciding whether to use a vector data model or raster data model in your work it entirely depends on the data you have as input and what your goals are for displaying or analyzing the data.
Arcinfo workstation coverage users have a long history and appreciation for the role that topology plays in maintaining the spatial integrity of their data here are the elements of the coverage data model. All cells in a raster must be the same size, determining the resolution. Raster data is made up of pixels or cells, and each pixel has an associated value. In vector data, the basic units of spatial information are points, lines and polygons. What kind of applications would each be most suited to.
As well, topology is static, and any updating or editing of the vector data requires rebuilding of the topology. So if you consider creating a data structure for rastor it would be a 2d array, each x,y coordinate refer a square in the are and it can have a certain predefined characteristic e. Fast the spatial database structure had to be really, really fast in terms of all crud operations. Many useful analyses do not require data with precise planar topology, but these analyses are never conducted because it is assumed that base data must have topology. Vertex dictionary no duplication, but still this model does not use topology figure 7. Digitising is the process of creating digital vector data by drawing it in a gis application. The following few sections provide an overview of raster and vector data structures as well as topology. List advantages and disadvantages of vector and raster data for gis. Raster images can contain one or more bands, each covering the same spatial area, but containing different information.
Lecture 1 intro to gis and gis vector and raster data models. Space is modeled as a grid of equalsized cells each cell is referenced by its row and column location the origin is the upper lefthand corner for most raster data because the location of each cell is known, this data structure has an implicit topology does not have. Space is modeled as a grid of equalsized cells each cell is referenced by its row and column location the origin is the upper lefthand corner for most raster data because the location of each cell is known, this data structure has an implicit topology does not have attribute tables uses a lookup table instead. In a coverage, the feature boundaries and points were stored in a few main files that were managed and owned by arcinfo workstation. A common use of raster data in a gis is as a background display for other feature layers. What is the overall problem facing the industry regarding formats. We will introduce a data structure for the hyperraster, which represents regions.
Traditionally, there are two broad methods used to store data in a gis for both abstractions. Here the issue is to receive the request and compile the map from standard. So, topology is a structure or data structures are having advantages. For polygon features, shapefiles and coverages have very different spatial data structures.
What are raster and vector data in gis and when to use. Topology is fundamentally used to ensure data quality of the spatial relationships and to aid in data compilation. In the vector world, we have points, lines and polygons that consist of vertices and paths. It is based on the anudem program developed by michael hutchinson 1988, 1989, 1996, 2000, 2011. The greatest differences can be shown comparing how polygons are stored.
Describe raster to vector and vector to raster conversion. Find, read and cite all the research you need on researchgate. Raster data models incorporate the use of a gridcell data structure where the geographic area is divided into cells identified by row and column. Topology is an informative geospatial property that describes the connectivity, area definition, and contiguity of interrelated points, lines, and polygon. Within a gis, the uses of raster data fall under four main categories. Also, you dont have the flexibility with raster data attribute tables. Discrete soil, land use, cities continuous elevation or rain fall. In gis, vector and raster are two different ways of representing spatial data. There are two types of data models namely, vector and raster data. Graphic output is usually more aesthetically pleasing traditional cartographic representation.
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