Differences between the underlying data models help to explain the variation in results between raster and network based methods. Overall, there was little difference in the accuracy between interpolation methods at the resolutions tested and minimal departure from the original 10m raster. Raster data can be images raster images with each pixel containing a color value. Different types of raster models or raster representations. Raster data is cellbased and this data category also includes aerial and satellite imagery. Rasters often look pixelated because each pixel has its own value or class.
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. Raster data are derived from a grid based system of contiguous cells containing specific attribute information. Data are entered into a gis from various sources and using various methods. The range of operations for spatial data analysis supported by a gis depends on a geometric model of geoobjects point, line or polygon, b spatial data models vector or raster, c type of attribute data quantitative or qualitative, d objectives of analysis and e gis software package used. Raster data is usually represented in the form of regular array of grids covering the study region or area of interest.
Lecture 1 intro to gis and gis vector and raster data models. A data model in geographic information systems is a mathematical construct for representing geographic objects or surfaces as data. What are raster and vector data in gis and when to use. In addition to distance, you can also use any function of grid cell values e. 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. If the area is 100 km x 100 km and cell size is 10 m. Maidment, introduction to spatial hydrology esri campus continuous surfaces can be represented using the grid or raster data model in which a mesh of square cells is laid over the landscape and the value of the variable defined for each cell. Gridcell systems are very compatible with raster based output devices, e. 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. Comparing methods for interpolation to improve raster. Built from at least two points at the ends of the line.
The gis spatial data model university of washington. For finer resolution and multi band data sets, the storage requirement grows exponentially. Vector data model representations of the real world source. 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. The data base concept is central to a gis and is the. In its simplest form, a raster consists of a matrix of cells or pixels organized into rows and columns or a grid where each cell contains a value representing information, such as temperature. Raster data models and comparisons with vector youtube. Index introduction components of gis data types in gis data representation raster data model vector data model differences between raster and vector triangulated irregular network tin digital elevation model dem conclusion reference. Here the purpose of a spatial data model is to provide a formal. For raster positions, its simple to understand cell size. Alternatively, each value in an elevation map represents a.
Suitability analysis with raster data by chris wayne, esri olympia this exercise, the first of a twopart series, will teach you how to work with raster layers using the arcgis spatial analyst extension. Each pixel value in a satellite image has a red, green and blue value. Types of raster data model advantages, disadvantages. 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. Raster model properties of uniformly spaced grid cells o typically represented as a twodimensional xy. In contrast to the raster data model is the vector data model. Raster data is cell based and this data category also includes aerial and satellite imagery. Mar 11, 2020 note that raster operations in arcmap are not covered on this years test but knowing the difference between raster and vector models is covered feedback on homework and labs rida slides shown in lecture.
Raster models are useful for storing data that varies continuously, as in an aerial photograph, a satellite image, a surface of chemical concentrations, or an elevation surface. Shapefiles are easily moved or copied within the os. Raster data also known as grid data represents the fourth type of feature. Other raster data, such as elevation models, can be mapped to color ramps that display elevation ranges, as shown in the image directly above. Differences between the underlying data models help to explain the variation in results between raster and networkbased methods. In raster, data is represented as a grid of usually square cells. Vector data models for gis up to now vector data models model boundaries of spatial features vector feature types.
Raster data models present information through a grid of cells raster grids are usually made up of square or rectangular cells. Vector data models use points and their associated x, y coordinate pairs to represent the vertices of spatial features, much as if they were being drawn on a map by hand aronoff 1989. Most gif files have a limit of 256 unique values this is known as 8bit data, because 28 256. What is the difference between vector and raster data models. Sep 03, 2016 raster data model and comparisons with vector. Vector representation of data in the vector based model, geospatial data is represented in the form of coordinates.
Pdf the raster data model is a widely used method of storing geographic. 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. Types of raster data model advantages, disadvantages just. Considering that the choice of data modelmethod may substantially alter the outcomes of a geographic accessibility analysis, we advise researchers to use caution in model selection. Continuous surfaces can be represented using the grid or raster data model in which a mesh of square cells is laid over the landscape and the value of the. Raster data models consist of 2 categories discrete and continuous. Measured real values an be integer or floatingpoint decimal values. One of the main disadvantage of raster data model is data storage. Unlike vector data models, which show geographic data through points, lines, or polygons, raster data is displays one value in each cell. Data can be represented at its original resolution and form without generalization. In this example from soller and others 1999, the upper surface of each buried geologic unit was represented in raster format as an arcinfo grid file. The spatial resolution of a raster dataset represents a measure of the accuracy or detail of the displayed information.
Both vector and raster data can be further classified based on the data content. Nov 26, 2017 raster data can be images raster images with each pixel containing a color value. The proof lies in considering some basic capabilities. Vector product format vpf is a standard format for a large geographic database based on georelational data models. A representation of the world as a surface divided into a regular grid of cells. However, it is possible to represent the data present in the study region in different ways as shown below. The result is a new table of cell values for each grid cell. The content of the lecture are the following, comparison of object view and field view, and related vector model and raster model will be discussed. Overall, quantitative analysis is intuitive with discrete or continuous rasters. The model most commonly takes the form of a gridlike structure that holds values at regularly spaced intervals over the. Although vector data can look like raster data on a map, the two are fundamentally different for analysis. Each grid cell is filled with the measured attribute values. A simple rasterbased model for flood inundation simulation. Data models for gis gis and geocomputation for water.
Raster data models present information through a grid of cells. The model is designed to operate with highresolution raster digital elevation models, which are becoming increasingly available for many lowland floodplain rivers and is based on what we hypothesise to be the simplest possible process representation capable of simulating dynamic flood inundation. Vector data is focused on modeling discrete features with precise shapes and boundaries. Raster grid format is data model for satellite data and other remote sensing data.
They are usually regularlyspaced and square but they dont have to be. Vector models are useful for storing data that has discrete boundaries, such as country borders, land parcels, and streets. Raster data is made up of pixels also referred to as grid cells. Vector data structure can be grouped into four classes namely. An example of discrete raster data is population density. All contemporary geographic information system incorporates a data base management system.
Buffering raster data classify grid cells according to whether they lie inside or outside the buffer. If one byte is used per pixel, it requires 100 mb storage ags 722 types of raster data 1. 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. 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. Discuss components of spatial data centers for disease. Satellite imagery remotely sensed satellite data are recorded in raster format. Vector data represents features as discrete points, lines, and polygons. Raster data models are used to represent a wide variety of phenomena, including continuous data like surface temperature or elevation. Raster data are derived from a gridbased system of contiguous cells containing specific attribute information.
For example, the vector data model represents geography as collections of points, lines, and polygons. In this model, space is not quantized into discrete grid cells like the raster model. Introduction rasterbased digital elevation models dems are an important data source used in a variety of spatial analyses. Tin data model and comparisons with raster duration. Raster models are useful for storing data that varies continuously. For raster data, this is the size of the individual cell or.
Gridcell systems are very compatible with rasterbased output devices, e. Rasters are digital aerial photographs, imagery from satellites, digital pictures, or even scanned maps. In this paper the development of a new model for simulating flood inundation is outlined. There are two primary types of spatial data models. Raster data compression models raster data encoding. It needs 10,000 rows x 10,000 columns or 100,000,000 pixels. Raster grids are usually made up of square or rectangular cells.
Huge space is required for storing data depending on the resolution of raster. Raster twister model builder demo and data raster twister tools toolbox. In vector data, the basic units of spatial information are points, lines and polygons. 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. Data models in geographical information systemgis 1. Simple features, topological features, network data model tin data model, georelational data model and objectbased data model in. Map algebra with raster data is usually quick and easy to perform. The raster data model is widely used by nongis technologies such as digital cameraspictures and lcd monitors. This value can be interpreted to mean several different things. Spatial data models geographic information system gis.
And vector model will be investigated in more detail. For example, elevation surfaces, temperature and lead contamination. The raster data model is a widely used method of storing geographic data. A raster dataset is the same type of image that is produced when recording an image with a digital camera. You will be creating and converting grid layers to prepare them for input into an analysis model. There are several advantages and disadvantages for using either the vector or raster data model to store spatial data. Raster based stacked surfaces depict the surface of each buried geologic unit, and can accommodate data on lateral variations of physical properties. Simple features, topological features, network data model tin data model, georelational data model and object based data model in.
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