A physical entity is represented by a spatial object in a gis. Vector data can have quality issues such as undershoots, overshoots and slivers which you need to be aware of. 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. Why do we have so many types of data formats, and why are they so difficult to use together.
Attribute data the information linked to the geographic features spatial data describing them. Every house, every tree, every city has its own unique latitude and longitude coordinates. 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. Vector representation vector representation of data in the vector based model figure 4, geospatial data is represented in the form of coordinates. Raster gis databases are arrangements of grid cells or pixels that are referenced by row and column positions. Vector data utilizes points, lines, and polygons to represent the spatial features in a map. Different types of vector data and concept of topology nptel. Advantages of vector data models over raster model answers. What are raster and vector data in the gis context.
Raster datasets can become potentially very large because they record values for each cell in an image. Also, you dont have the flexibility with raster data attribute tables. Cellby cell encoding a raster model is stored as a matrix. Data analysis since most input data does not exist in a topological data structure, topology must be built with the gis software. 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. 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. Learn vocabulary, terms, and more with flashcards, games, and other study tools. While the structure of raster data is simple, it is exceptionally useful for a wide range of applications. Raster data models incorporate the use of a gridcell data structure where the geographic area is divided into cells identified by row and column. In the vector world, we have points, lines and polygons that consist of vertices and paths. 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.
Within the spatial referenced data group, the gis data can be further classified into two different types. While the term raster implies a regularly spaced grid other tessellated data structures do exist in grid based gis systems. A raster representation for scalable image and volume data. It provides a more compact data structure than the raster model. As resolution increases, the size of the cell decreases. What is the overall problem facing the industry regarding formats. As well, topology is static, and any updating or editing of the vector data requires rebuilding of the topology. It uses topology spatial relationships to represent spatial objects in addition to the use of geometry coordinates thorough adjacency, containment. The spatial resolution of a raster dataset represents a measure of the accuracy or detail of the displayed information. The model most commonly takes the form of a gridlike structure that. Divides space into discrete features, usually points, lines or polygons. 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. Real world objects can be divided into two abstractions.
Coding best works when neighboring pixels are similar 2. List advantages and disadvantages of vector and raster data for gis. This slide gives a graphic example of how the vector data structure is stored using the spaghetti data structure. The gis spatial data model university of washington. Raster structures runlength encoding the storage requirements for full raster images increase geometrically with the decreasing size of a pixel causing storage space problems this requires compression methods runlength encoding is a simple data structure that can reduce the space requirements of some images drastically. Each grid cell is filled with the measured attribute values.
The advantages and disadvantages of vector and raster data. Spatial data can represent vector and raster data models realworld features that have discrete boundaries such as roads, buildings, lakes, rivers, administrative. Does anyone have some small, concise, effective pictures which convey and contrast these two fundamental data representations. Introduction to gis basics, data, analysis case studies. 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. Topological connections may be quite important when rasters are. Raster data structure refers to storage of raster data so that it can be processed by the computer. Raster data are good for showing continually varying information.
This contributes to the merging of raster and vector operations. The size of pixels in a raster determines its spatial resolution. There are many analysis that make use of both data models i. Discrete soil, land use, cities continuous elevation or rain fall. The data base concept is central to a gis and is the main difference between a. Find, read and cite all the research you need on researchgate. 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. There are two types of geodatabases freely available to all arc users, personal geodatabases and file geodatabases.
Notice along the shared boundary between the parcels, the coordinates for the boundary are stored redundantly. 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. 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. Vector data can be used for spatial analysis in a gis application, for example to. Introduction to gis and spatial data vector and raster comparison vector raster compact data structure for homogenous areas. Topology is fundamentally used to ensure data quality of the spatial relationships and to aid in data compilation. Deltamapgenamap tiled topological and coverage raster data. There are two broad categories of spatial data models. As well as employing the raster and vector spatial data models1 we.
These are vector data model and raster data models. Difficult to resolve fine details little to no variation of values of large area. Data can be represented at its original resolution and form without generalization. Within a gis, the uses of raster data fall under four main categories. 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. 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. Lecture 1 intro to gis and gis vector and raster data models.
Idrisi and other software is based on the vector spatial data model e. 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. Each cell must be rectangular in shape, but not necessarily square. L155 gis data models and data processing lecture 3 dr. So, topology is a structure or data structures are having advantages. Here the issue is to receive the request and compile the map from standard. 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. Raster data are derived from a gridbased system of contiguous cells containing specific attribute information. 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.
Now a spatial data can be divided in 3 main categories. Digitising is the process of creating digital vector data by drawing it in a gis application. In vector data, the basic units of spatial information are points, lines and polygons. We will introduce a data structure for the hyperraster, which represents regions. 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 particular, the quadtree data structure has found some. Traditionally, there are two broad methods used to store data in a gis for both abstractions.
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. The greatest differences can be shown comparing how polygons are stored. 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. The following few sections provide an overview of raster and vector data structures as well as topology. Raster data is made up of pixels or cells, and each pixel has an associated value. Furthermore, topology is static, and any editing of the vector data requires rebuilding of the topology.
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. Raster is often background visualization for vector data courtesy of. 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. A simple data structurea matrix of cells with values, representing a coordinate, and sometimes linked to an attribute table. What kind of applications would each be most suited to. The raster data model is widely used by nongis technologies such as digital cameraspictures and lcd monitors. This building process involves the creation of the topological tables and the definition of the arc, node, and polygon entities. In general terms what applications, processes, or analysis are each suited for. File geodatabase are more current and exhibit several advantages over personal. Also, topology among graphical objects or items are much easier to be. All cells in a raster must be the same size, determining the resolution. The topo to raster tool is an interpolation method specifically designed for the creation of hydrologically correct digital elevation models dems. Graphic output is usually more aesthetically pleasing traditional cartographic representation. In an enterprise geodatabase, raster data is stored in a structure where the data is tiled, indexed, pyramided, and most often compressed.
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. It provides efficiently encoding of topology and as result more efficiently. In a coverage, the feature boundaries and points were stored in a few main files that were managed and owned by arcinfo workstation. Jan 14, 2011 for effective analysis, vector data must be converted into a topological structure. Fast the spatial database structure had to be really, really fast in terms of all crud operations. 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.
In the raster world, we have grid cells representing real world features. Raster data structure refers to the method or format for storing raster data so that it can be used efficiently. For polygon features, shapefiles and coverages have very different spatial data structures. Simulation easy, because cells have the same size technology is cheap disadvantages of raster data structures. Its cell values are written into a file by row and column.
What is the difference between vector and raster data. Vector representation of data in the vector based model, geospatial data is represented in the form of coordinates. Length encoding quad tree used when values change continuously cell. 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. Raster and vector are the two basic data structures for storing and. However, the distinction between vector and raster data types is not unique to gis. Describe raster to vector and vector to raster conversion. Each area is divided into rows and columns, which form a regular grid structure. Spatial data types provide the information that a computer requires to reconstruct the spatial data in digital form. 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.
In rastor, the area under consideration is divided into equal squares and a characteristic assigned to it. Spatial concepts, geometric data models and data structures, in d. Which vector formats have been created by the government. Vector data may or may not be topologically explicit, depending on the files data structure. Although this may be heresy to many users, there are advantages to using shapefiles that violate planar assumptions i.
Raster is a method for the storage, processing and display of spatial data. But this comes at a cost for speed of processing and data storage. Topology in raster and vector representation springerlink. Vector and raster data both have their advantages and disadvantages. Spatial data models and structures semantic scholar. 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. Data volume and redundancy dense grid of data involves large memory requirements and computer power. The details of all publications are in the researchgate in full text pdf forms.
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. A raster is an array of cells, where each cell has a value representing a specific portion of an object or a feature. Applying functions, the hybrid raster elements need not be stored. A common use of raster data in a gis is as a background display for other feature layers. Deltamapgenamap tiled topological and coverage raster. 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. Vector data models structures vector data models can be structured many different ways. It becomes thus possible to determine the topological relation of two regions, given in raster representation, with the same reasoning as in vector representations. For effective analysis, vector data must be converted into a topological structure.
Raster images can contain one or more bands, each covering the same spatial area, but containing different information. Exploring data structures 2 geodatabases can have behaviors detailed within the data structure to better model realworld relationships. Pdf topology in raster and vector representation researchgate. The simplest use of dynamic might be the case of dynamically generated maps, for example on a web site or a gpsbased navigation system. Whats the difference between gis spatial data types. 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. Topology is an informative geospatial property that describes the connectivity, area definition, and contiguity of interrelated points, lines, and polygon.
There are two types of data models namely, vector and raster data. Pdf the raster data model is a widely used method of storing geographic data. Vertex dictionary no duplication, but still this model does not use topology figure 7. What are raster and vector data in gis and when to use.
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