In a raster data set, data values for a given parameter are stored. The raster approach is better for delineating continuous geographic fields of. A data model in gis is a mathematical construct for representing geographic objects or surfaces as data. Divides space into discrete features, usually points, lines or polygons.
The size of pixels in a raster determines its spatial resolution. Raster images can contain one or more bands, each covering the same spatial area, but containing different information. Aug 16, 2017 this tutorial is about vector and raster data in gis that how to understand the difference between vector and raster data structures. Lecture 2 introduction to gis based on lecture notes of. Introduction to gis and spatial data vector and raster comparison vector raster compact data structure for homogenous areas. These are vector data model and raster data models. You can think of them as a cartographic view of your geographic. Raster and vector are the two basic data structures for storing and. The great diversity of spatial data structures is one of the reasons why exchanging spatial data between gis is problematic.
Raster grids are usually made up of square or rectangular cells. This value can be interpreted to mean several different things. The data base concept is central to a gis and is the main difference between a gis and drafting or computer mapping systems, which can produce only good graphic output. Changs chapter 7 elements of the raster data model. Therefore, the connection between raster and vector data is critical in spatial hydrology, perhaps more so than in other applications of gis. Discuss components of spatial data centers for disease.
In gis, vector and raster are two different ways of representing spatial data. Raster grid format is data model for satellite data and other remote sensing data. What is the difference between vector and raster data models. There are two major types of geometric data model a. Traditionally spatial data model has been stored and presented in the form of a map. Raster data model data model user group join the data model user group if you are an existing arcgis customer and want to learn more about design and architecture of personal or enterprise geodatabase and become a part of esris growing data model community. How the data is stored in the database, the applications that access it, and the client and server hardware configurations are all key factors to a successful multiuser geographic information system gis. This makes vector data structure the apparent choice for most mapping, gis and. A raster is an array of cells, where each cell has a value representing a specific portion of an object or a feature. Data processing steps modelbuilder creates visuals of your procedure what is stored where the gis project maintains links to the individual data files the data is not embedded in the map document itself gis formats, like shapefile shp, have many files that are linked together and must stay together in order to function. Care should be taken to determine whether the raster or vector data model is best suited for your data andor analytical needs. Click next to arrive at the window shown at the right. There are two types of data models namely, vector and raster data models.
Point, polyline and polygon features work well for representing some features. Successfully implementing a gis with arcinfo and arcsde starts with a good data model design. The raster data model is widely used by nongis technologies such as digital cameraspictures and lcd monitors. Elevation, as a continuous land field characteristic, is usually stored in a vector file for easier data management, but is more suitable to be represented by a. There are two essential methods used to store information in a geographic information system gis for both reflections. The vector model uses points and line segments to identify locations on the earth. Unlike vector data models, which show geographic data through points, lines, or polygons, raster data is displays one value in each cell. The raster data model is widely used to encode gis data. These features are the basic features in a vectorbased gis, such as arcgis 9. 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. Each gis file along with spatial features also contains a table in which each row record. Introduction to gis 10 the data bases used in gis are most commonly relational. Models are composed of a mix of raster, vector, and attribute data.
Two data models commonly used to represent spatial data in gis are the raster and vector data models within the vector data model, a representation of the world is created using lines, points, and polygons. Lidar point cloud data is also available over many areas of the us. Raster data are derived from a gridbased system of contiguous cells containing specific attribute information. The raster data model is a convenient way of modeling other geographic relationships, as well. Giss have traditionally used either raster or vector for maps. The two basic data models of gis are raster and vector. Elevation, as a continuous land field characteristic, is usually stored in a vector file for easier data management, but is more suitable to be represented by a raster data model. Raster model vector model points, lines, polygons features and maps a gis map is a scaleddown digital representation of point, line, area, and volume. Resolution depends on real world area represented by each grid cell. Each grid cell is filled with the measured attribute values. Each of these models has its own advantages and disadvantages. Overall, quantitative analysis is intuitive with discrete or continuous rasters. If the area is 100 km x 100 km and cell size is 10 m. For raster positions, its simple to understand cell size.
Introduction to gis basics, data, analysis case studies. What is the difference between vector and raster data. The old gis adage raster is faster, but vector is corrector comes from the two different fundamental gis models. For example, the vector data model represents geography as collections of points, lines, and polygons. Raster and vector data model in gis there are two essential methods used to store information in a geographic information system gis for both reflections. Overview of raster data model raster data models define objects in a fixed manner see figure 1. See that red box that has been sitting on top of the raster layer. Pdf the raster data model is a widely used method of storing geographic data. Some personal computer pc packages utilize vector structures for data input, editing, and display but convert to raster structures for any analysis. A perfect copy of reality cannot be recreated in the computer. The gis spatial data model university of washington. Jun 06, 2017 conclusion geographic information system is a computer system for capturing, storing, checking, and displaying data related to positions on earths surface.
A common use of raster data in a gis is as a background display for other feature layers. Within a gis, the uses of raster data fall under four main categories. Raster data is made up of pixels or cells, and each pixel has an associated value. The national hydrography datasets, watershed boundary dataset, governmental boundary units, transportation, structures, elevation contours and geographic. All contemporary geographic information system incorporates a data base management system. The cells pixels, picture elements are constant in size and are generally square. Rasters as basemaps a common use of raster data in a gis is as a background display for other feature layers. Vector model vector model uses discrete points, lines andor areas corresponding to discrete objects with name or code number of attributes. Raster data consists of rows and columns of cells or pixels. See our dataset list for a brief explanation of these products. Conclusion geographic information system is a computer system for capturing, storing, checking, and displaying data related to positions on earths surface.
What is the meaning of data model, vector, vector data, model, gis. Vector representation vector representation of data in the vector based model figure 4, geospatial data is represented in the form of coordinates. Each layer of grid cells in a raster model records a separate attribute. Staged productsthe topographic maps and geographical information system gis data provided in the national map are pregenerated into downloadable products often available in multiple formats. Vector data model the three main geometric shapes used in the vector data model, to represent real world features are. Raster model divides the area into grid cells or pixel. Gis data represents realworld objects such as roads, land use, elevation with digital data. The basic spatial data model is known as arcnode topology. Layer files reference geographic data stored on disk. Simple data structures overlay and combination of maps and remote sensed images easy some spatial analysis methods simple to perform simulation easy, because cells have the same size technology is cheap disadvantages of raster data structures. A data model in geographic information systems is a mathematical construct for representing geographic objects or surfaces as data. Raster data model represents phenomena as occupying the cells of a predefined, grid shaped tessellation. It is often difficult to compare or rate gis software that use different data models. The raster data model is a widely used method of storing geographic data.
An element of the grid cell is called a pixel which contains a. Rasters have a new home in the geodatabase since arcgis 9. Raster data models present information through a grid of cells raster grids are usually made up of square or rectangular cells. Raster model raster model uses regularly spaced grid cells in specific sequence. The data model a logical data model is how data are organized for use by the gis. Gis and modeling overview the term modeling is used in several different contexts in the world of gis, so it would be wise to start with an effort to clarify its meaning, at least in the context of this book. Rasters are spatial data models that define space as an array of equally sized cells, arranged in rows and columns, and composed of single or multiple bands. Instead, vector graphics are comprised of vertices. Lecture 1 intro to gis and gis vector and raster data models. Gis refers to those spatial information systems that are used for processing and analyzing geospatial data. Raster data model each grid cell in a raster data layer is one unit the minimum amount of information in the raster data model every cell has a value, even if it is a special value to indicate that there is no data or that data is missing at that location the values are numbers, either. Spatial data features in a, typically points, lines or areas polygons. Much raster data is already in digital form, as images, etc. Raster data are good for showing continually varying information.
In this unit, we will discuss the basic concepts of raster and vector data models in gis. Integrated with the geoprocessing framework, arcgis spatial analyst offers easy access to numerous functions in modelbuilder, a graphic modeling tool. Different gis may contain information of value to the other, but will be 1the term data model is often used to describe these two terms. Lecture 2 introduction to gis based on lecture notes of dr. Nov 26, 2017 there are two essential methods used to store information in a geographic information system gis for both reflections. Piotr jankowski, former professor in department of geography at ui objective the purpose of this lecture is to provide an introduction to gis and give an overview of basic theoretical and technical concepts in gis. Vector data is focused on modeling discrete features with precise shapes and boundaries. The raster data structure is an approach for encoding spatial data computationally for use within a geographic information system gis or remotely sensed. Data processing steps modelbuilder creates visuals of your procedure what is stored where the gis project maintains links to the individual data files the data is not embedded in the map document itself gis formats, like shapefile shp, have many files that.
In many cases, you would like to subset your raster data to an area defined by one of your vector data layers. The model most commonly takes the form of a gridlike structure that. If one byte is used per pixel, it requires 100 mb storage ags 722 types of raster data 1. It needs 10,000 rows x 10,000 columns or 100,000,000 pixels.
The model most commonly takes the form of a gridlike structure that holds values at regularly spaced intervals over the. This tutorial is about vector and raster data in gis that how to understand the difference between vector and raster data structures. While the structure of raster data is simple, it is exceptionally useful for a wide range of applications. Map algebra with raster data is usually quick and easy to perform. 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. A physical entity is represented by a spatial object in a gis. Digital elevation models dems, orthoimagery, and land cover. Raster data models present information through a grid of cells. That is the study extent that all but the raster layers have been clipped to in the tutorial data. The raster data model is widely used by non gis technologies such as digital cameraspictures and lcd monitors.
Vector model boundaries of spatial features our focus so far. Raster model spatial data of different types can be overlaid without the need for the complex geometric calculations. Point line points, lines and polygons are polygon stored in separate, point, line, and polygon, gis files. In vector data, the basic units of spatial information are points, lines arcs and polygons. Data models in gis raster data model vector data model triangulated irregular network model tin digital elevation model dem network models 10. One of the strengths of the vector data model is that it can be used to render geographic features with great precision. Vector and raster data difference between raster and. A short and sweet description of the two data models and how they handle object versus discrete phenomena. It is unnecessary to store the coordinates of each cell as the. Satellite imagery remotely sensed satellite data are recorded in raster format.
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