Although vector data can look like raster data on a map, the two are fundamentally different for analysis. Geographic information system gis is a computerbased tool or technology to manage, analyze and display geographically referenced information. 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. Raster data storage uses square cells to model points, lines, or areas continuously. Types of raster data model advantages, disadvantages just.
Comparison of raster and vector data models raster model advantage. The raster format is more or less required for efficient manipulation and enhancement of digital images. Mar 01, 2019 the main difference between raster and vector data is that the raster data represents data as a cell or a grid matrix while vector data represents data using sequential points or vertices. Vector data may or may not be topologically explicit, depending on the files data structure. Hijmans april 5, 2012 1 introduction this vignette describes the r package raster. In all cases, the geometry of these data structures consists of sets of coordinate pairs x, y. In particular, the quadtree data structure has found some. Overlay operations are easily and efficiently implemented.
Raster data model makes use of regular array or matrix of cells of uniform size and shape for representing data. What is the difference between raster pdf file and vector pdf. The raster data model consists of rows and columns of equally sized pixels interconnected to form a planar surface. While the term raster implies a regularly spaced grid other tessellated data structures do exist in grid based gis systems. For purposes of visualization a lookup table has been used to. 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. Weerakaset suanpaga,ku raster layers of different cells sizes 18 dr. To the contrary,vector structure has compact form,low redundancy rate,and it is convenient for net and searching analysis,can reveal image with high. By rearranging the data transfer flow, establishing an integrated vector and raster data model, and optimizing the spatial data retrieval mechanism, this system enabled united storage and. This data structure is applied to the data with continuous changes because it is hard to be cut into independent points, lines, and polygons. Ltd, 2nd edition, universities press orient longman pvt. The raster data model is a widely used method of storing geographic data.
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. Due to the nature of the data storage technique data analysis is usually easy to program and quick to perform. Spatial data structures spatial data types provide the information that a computer requires to reconstruct the spatial data in digital form. 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.
In the example the cells of tessellation a are overlaid on the point pattern b resulting in an array c of quadrant counts representing the number of points in each cell. What is the difference between raster pdf file and vector. Weerakaset suanpaga,ku raster layers of different cells sizes. Sometimes raster data are created from vector data because the data owners want to share the data in an easy to use format. Any shape can be used that will completely fill an area. Raster images are stored in image files with varying formats. Raster data structure refers to the method or format for storing raster data so that it can be used efficiently. Data structures pdf notes ds notes pdf eduhub smartzworld. Its cell values are written into a file by row and column. The raster data structure is an approach for encoding spatial data computationally for use within a geographic information system gis or remotely sensed. A raster data structure is based on a usually rectangular, squarebased tessellation of the 2d plane into cells. 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. Understanding raster data introduction what is raster data. Allows for efficient encoding of topology, and as a result more.
Remember that floating point numbers typically use up more storage space. Through the description of the above,we can see that raster structure is simple and convenient for spatial analysis,but its data volume is huge,and projection transformation seems complicated. Vector representation vector representation of data in the vector based model figure 4, geospatial data is represented in the form of coordinates. Rasters are digital aerial photographs, imagery from satellites, digital pictures, or even scanned maps. In an enterprise geodatabase, raster data is stored in a structure where the data is tiled, indexed, pyramided, and most often compressed.
The model most commonly takes the form of a gridlike structure that. Vector data tend to be more compact in data structure, so file sizes are typically much smaller than their raster counterparts. The raster data represent the same vector polygon at 30 m and 90 m cell resolution. Vector data utilizes points, lines, and polygons to represent the spatial features in a map. For many natural phenomena, such as elevation, air temperature of air and water, the depth of groundwater, and the distribution of pollution, there are no clear boundaries among them. A home becomes a cell with a value that represents homea river becomes a cell with a value that represents rivera stand of trees becomes a group of cells all with a value that. 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 common use of raster data in a gis is as a background display for other feature layers.
Many people use raster data as a backdrop to be used behind vector layers in order to provide more meaning to the vector information. Types of raster data model advantages, disadvantages. In computer graphics, a raster graphics or bitmap image is a dot matrix data structure that represents a generally rectangular grid of pixels points of color, viewable via a monitor, paper, or other display medium. Raster data structure header dimension and spatial resolution projection and coordinates thumbnails data types.
Basically data structure is identical in both categories. I have tried to convert a raster to a dataframe on one file just to see if it works. The raster data model jackson school of geosciences. A raster is a spatial geographic data structure that divides a region into rectangles called cells or pixels that can store. In general, vector data structure produces smaller file size than raster image because a raster image needs space for all pixels while only point coordinates are stored in vector representation. Raster data also known as grid data represents the fourth type of feature.
Data structuredata structure in data structure in gis gis. This is particularly true in the case when the graphics or images have large homogenous regions and the boundaries and shapes are the primary interest. Within a gis, the uses of raster data fall under four main. 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. Graphic output is usually more aesthetically pleasing traditional cartographic representation. The raster product format rpf is a standard data structure developed in 1994 as a u.
Continuous data change smoothly across a landscape or surface. Introduction to gis and spatial data vector and raster comparison vector raster compact data structure for homogenous areas. The model most commonly takes the form of a gridlike structure that holds values at regularly spaced intervals over the extent of the raster. Rasters are especially well suited for storing continuous data such as temperature and elevation values. While the structure of raster data is simple, it is exceptionally useful for a wide range of applications. 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. Discuss components of spatial data centers for disease. Raster and vector are the two basic data structures for storing and manipulating images and graphics data on a computer. A raster is a spatial geographic data structure that divides a region into rectangles called cells or pixels that can store one or more values for each of these cells.
Lecture 1 intro to gis and gis vector and raster data models. The digital photographs we see in our everyday life, satellite imagery, aerial photographs etc. Data is represented at original resolution and form without generalization. In vector data, the basic units of spatial information are points, lines arcs and polygons. Military standard for geospatial databases composed of rectangular arrays of pixel values e. Topology is an informative geospatial property that describes the connectivity, area definition, and contiguity of interrelated points, lines, and polygon. Rasters often look pixelated because each pixel has its own value or class. Jul 12, 2012 raster data structure is suitable for recording natural phenomena with continuous changes, like temperature and elevation.
What are raster and vector data in gis and when to use. Difference between raster and vector raster vector it is a simple data structure. Vector data structure topological data structure points are vertices a line is a sequence of ordered vertices, where the beginning 0f the line is a special vertex or start node and the end a special vertex called an end node a chain is a line which is part of one or more polygons, they are also called arcs or edges. Phenomena such as chemical concentration, slope, elevation, and aspect are dealt with in raster data structures far better than in vector data structures. In rastor, the area under consideration is divided into equal squares and a characteristic assigned to it. Raster data is cellbased and this data category also includes aerial and satellite imagery. Raster data is made up of pixels also referred to as grid cells. Raster data models incorporate the use of a gridcell data structure where the geographic area is divided into cells identified by row and column. Raster data model is conceptual model used in gis for representing real world entities or phenomena. Introduction to gis basics, data, analysis case studies.
A raster can represent thematic data or raster images. Raster and vector are the two basic data structures for storing and manipulating images and. Measured real values an be integer or floatingpoint decimal values. Raster gis databases are arrangements of grid cells or pixels that are referenced by row and column positions. How raster data is stored and managedhelp arcgis for desktop. The model most commonly takes the form of a gridlike structure that holds values at regularly spaced intervals over the. Alternatively, each value in an elevation map represents a. 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. The vector data were developed using onscreen digitizing with national agriculture imagery program naip as the background. Here you can download the free data structures pdf notes ds notes pdf latest and old materials with multiple file links to download. High spatial variability is efficiently represented in a raster format. For example, a company with road, rail, cadastral and other vector datasets may choose to generate a raster version of these datasets so that employees can view these datasets in a web browser. High spatial variability is efficiently represented in raster format. An example of discrete raster data is population density.
Each pixel value in a satellite image has a red, green and blue value. A raster is an array of cells, where each cell has a value representing a specific portion of an object or a feature. Cellby cell encoding a raster model is stored as a matrix. Length encoding quad tree used when values change continuously cell. Raster data structure refers to storage of raster data so that it can be processed by the computer. 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.
Sections describing raster data models, tin data models, and data structure then follow. Raster data model the data model critical decision is the choice of the data model, which is the basis of a gis different data models are required for spatial and attribute. 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. Advantages simple data structure resolution is set by cell size easily modified displayoutput good for images faster and very efficient for overlay operation raster data mainly is obtained from satellite images and scanning raster is utilized when data change continuously across a region high spatial variability is efficiently represented. The main difference between raster and vector data is that the raster data represents data as a cell or a grid matrix while vector data represents data using sequential points or vertices geographic information system gis is a computerbased tool or technology to manage, analyze and display geographically referenced information. The proof lies in considering some basic capabilities.
These pixels are used as building blocks for creating points, lines, areas, networks, and surfaces chapter 2 map anatomy, figure 2. Users can visualize, and understand the relationships. Major gis and cad computer aided design software packages. 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. Raster file size can result larger in comparison with vector data sets with the same phenomenon and area. The human eye is very good at interpreting images and so using an image behind vector layers, results in maps with a. How raster data is stored and managedhelp arcgis for. In the case of floating points, pixels are representing continuous data. Although the ability of modern computers has minimized the importance of maintaining small file sizes, vector data often require a fraction the computer storage space when compared to raster data. All cells in a raster must be the same size, determining the resolution. The cells contain values or attributes for showing the variation of features. When raster data structure is used, the smaller the size of pixel or grid cell is, the higher resolution of spatial data comes and the more cells with the same attribute.
Raster images are stored in image files with varying formats a bitmap is a rectangular grid of pixels, with each pixels color being specified by a number of bits. Area estimates differ depending on data structure and resolution. The size of each cell depends on analyzed scales i. Raster data are especially suited to continuous data. Raster data structure is suitable for recording natural phenomena with continuous changes, like temperature and elevation. Data matrix see the in class example that you created above with the topo map.
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