3 What is a RASTER GIS?A graphic representation of features and attributesOften looks more like an image than a mapMade of grid cells which contain informationCells can be any size but are often limited by several criteria
4 Raster GIS represents elements of the real world for analysis: While feature themes use Coordinates and lines (vectors) to represent geographic featuresRaster Grid themes use cells to represent geographicfeatures
5 Vector GIS We have already used a vector based GIS It is superb at drawing mapsIt is excellent for managing attribute dataIt is very efficient for performing calculation along routes and for areas with matching geographies
6 In A Vector GIS... Points, Lines and Areas represent entities Points - City, TreeLines - River, RoadAreas - Forest, LakeAnalysis includes:BufferingIntersectingNetwork Analysis (shortest path)
7 Raster GIS Very different from the Vector GIS Uses more images and gridsStores data differentlyUses square grids to hold dataUses more “codes” to interpret dataUses much more processing powerCan generate many more mathematical outputs
8 In A Raster Based GIS... Raster Themes Include: Images Scanned maps, Air photos,Satellite imagesGridsDEM, Surfaces
9 In A Raster GIS... Grids represent entities Analysis Includes: Grids made of cellsValue applied to cellAnalysis Includes:Buffering/ProximityReclassificationHill-shade/SlopeInterpolationSurface Calculation
10 Tools for Raster Data Analysis... Map AlgebraHill ShadesSlopeAspectRaster ModelingRaster and Vector IntegrationRaster to polygon conversionContour GenerationSurface Interpolation from point data
11 How does it work? A imaginary grid is placed over an area Each cell in the grid is given a numeric code for the attribute that is dominant in that cellEach cell can be...numericqualitativea feature identifier
12 A Vector to Raster Comparison... Vector GIS Manages Discrete FeaturesDistinct boundariesStored as integer valuesLand use, zoning, vegetation, lakes, roads, riversVector ModelA Raster GIS Manages Continuous DataStores data as floating point valuesExamples: Elevation, noise pollution, rainfall, slope and temperatureRaster Model
13 The Raster GridRaster grids are always square but can be displayed as other shapesEach group of cells can be considered a layerVarious layers can be overlain on each otherCalculations can be done between layers if the grids line up.
14 Raster Grid Structure Row 1 2 3 Column Cell (2,3) Grid themes are an organized matrix of cellsCells are organized into rows and columnsRows and columns have an index position numberTop left cell is at the 0,0 positionCells Store a numeric valueNumeric values are codes that represent geographic features1-Wetlands2-Water3-Forest4-RecreationCells with the same value make up a zoneRow123ColumnCell (2,3)
15 Geographic AnalysisRaster systems are superb at analyzing some geography problems such as...Data that changes continuous over a surfaceelevationvegetationrainfalltemperature, etc.There can be used to create new information such as erosion potential.
16 Raster GIS Analysis Questions and answers about something geographic Leads to decisions that affect peopleInvolves budgeting money and resourcesSpatial query examplesShow me the pine treesSelect the freewaySpatial analysis examplesWhich trees are ready to harvest?Identify some corridors for the new freeway
17 What is GIS Analysis From simple to Complex Simple - Sometimes by just making a map you are doing analysisComplex - Sometimes we use many layers of data to simulate real world events
18 Data Analysis What can we map using GIS (Spatial Analysis Tools)? Map where things are- Location AnalysisMap the most and least- Quantitative AnalysisMap concentrations- DensityMap what is inside- MonitoringMap what is nearby- RelationshipsMap Change- Prediction
20 What are the effects of Global Warming? Land cover and temperature relationships are made clear when the data are seen at once.
21 Will the new building spoil the Park Scenery? Park planners use GIS to determine if a new Visitor Centre can be seen from the peak.
22 How can I reduce my fertilizer Input? GIS is used in making crop management decisions to maximize yields and minimize fertilizer input.
23 Managing Raster Data Raster systems are data intensive they must record data at every cell even if nothing is presentuse large amounts of hard drive spaceRaster systems have the advantage of being uniformly defined.This means that very powerful analytical tools can be used with a raster system.
24 Summary Raster systems use grids to store information Images are raster gridsImages can be given attributes by pixelGrid can be analyzed for various purposesRaster data can be overlaid with other grids for greater analysis power.
25 VECTOR! Vector Data Represented by point, line and polygon. Relatively small file size (small data volume)Excellent representation of networks.A large no. of attributes can be attached, hence more information intensive and a number of thematic maps can be prepared from a single layer.Features are more detailed & accurate.Creating, cleaning and updating data is more time and labour consuming.
26 Vector con’tTopology-based analysis & operations are easier to perform (like network analysis etc.).Can not represent continuous values like land use, elevation etc very well.Assigning projection and transformations are less time taking and consumes less memory of the computer system.Topology makes data structure complex.
27 RASTER! Points, line & polygons everything in the form of Pixels. Large file size.Networks are not so well represented. Only one pixel value represents each grid cell.Generalization of features (like boundaries) hence accuracy may decrease.Simulations and modeling is easier (spatial analysis, terrain modeling etc.).
28 Raster con’t Maintaining is easier. Excellent for representing data containing continuous values (like land use, elevation etc.)Coordinate-system transformations take more time and consume a lot of memory.Grid cells or pixel makes simpler data structure.