Spatial analysis in gis Prachi Sukumar Mehta MG 0712 Date: 7th February, 2013 CEPT University
WHY analyze using gIS?1. Visual representation of data – Human mind can comprehend better2. Vector data – precise, mathematical operations can be performed3. Database – Spatial data with non-spatial attributes4. Updatable – Easily can be modified, scaled5. In-built functionalities
What kind of analysis can be made using gis?• Map production• Geovisulization• Query, Measurement, Transformation• Descriptive Summary• Modeling
Cartography and map production• Cartography is both an art and a science.• GIS-based cartography makes it easier to create large numbers of maps very quickly using automated techniques once databases and map templates have been built.• Different type of data in different layers can help in controlling the information that is displayed.• Maps can be reused and recycled. Different datasets, obtained over a period of time can be useful in analyzing trends.
geovisualizationThere are four principal purposes of geovisualization:1.Exploration: for example, to determine the general message of adataset is affected by inclusion or exclusion of particular dataelements.2.Synthesis: To view to data in desired form.3.Presentation: Enable the user to understand the representation.4.Analysis: Support a range of methods and techniques of spatialanalysis.
Example of geovisualization : Cartograms Cartograms are map transformations that distort area or distance in the interests of some specific objective. Linear cartogram transformation of London Underground
Query, measurement and transformation • Spatial analysis can reveal things that might otherwise be invisible – it can make what is implicit explicit. • It helps us in situations when our eyes might otherwise deceive us. Reveals pattern, trends and anomalies.Queries : It makes no changes in the data.No new data is generated. It just displaysthe data in appropriate views.Two or more views can be linked orviewed together.
Measurement : Measurements on maps are various types.•Length and Distance•Area•Shape•SlopeSuch measurements are tedious and inaccurate if made by hand.Transformation : Creates new objects and attributes based on simple rules. Mayalso create new fields from existing fields or discrete objects. Buffering and PolygonOverlay are examples of transformation. Buffering Overlay
Descriptive summary• It is an attempt to summarize useful characteristics of data in one or two statistics• Mean, Median and Mode are widely used measures. E.g, Mean temperature in December• Centers are spatial equivalent of mean. Centers can be defined in several ways like Centroids, Minimum Aggregate Travel (MAT) etc. Centroid : Weighted average of MAT : Minimizes travel from a set of coordinates. Minimizes sum of distances points. Found by iteration squared.
Modeling• Models allow planners to experiment with ‘what-if’ scenarios.• Models can be used for dynamic simulation, providing decision makers with dramatic visualizations of alternative futures. Groundwater vulnerability model in an area of Ohio, USA. The model combines GIS layers representing that affect the groundwater, and displays the results as a map of vulnerability ratings• Any model forecast should be accompanied by a realistic measure of uncertainty.
Reference• Geographic Information Systems and Science (2E) by Paul A. Longley, Michael F. Goodchild, David J. Maguire, David W. Rhind