spatial analysis introduction and vector type of data.pdf
- 1. Module 3 Introduction to GIS Lecture 9 – Spatial analysis using GIS
- 2. GIS workflow Data acquisition (geospatial data input) •GPS •Remote sensing •Ortophotos •LiDAR Attribute Data Management •Data verification •Database management Exploratory Analysis •Attribute and spatial data queries •Geovisualization Data Analysis •Vector and raster data analysis •Terrain mapping •Spatial interpolation •Network analysis Geovisualization (maps) Chang, 2014, p.8-9
- 3. Spatial Analysis Toolbox Basic toolbox Spatial analysis (proximity, overlay) Projection transformation Attribute data management Surface creation Selection Extraction Geovisualization GIS software
- 4. Spatial analysis using vector, raster and attribute table Spatial analysis use the layers (vector or raster) to obtain new outputs and/or the database Vector analysis – Buffering (proximity analysis), Overlay and Distance Measurement. Raster analysis – Local operations (including reclassification) and Distance Measurement. Attribute analysis – Queries (basic – Identify; advanced – Query Builder) Spatial analysis operations different for vector and raster
- 6. Spatial analysis using vector The vector data model uses points and their (x,y) coordinates to construct spatial features of points, lines and polygons. Vector data analysis uses the geometric objects of point, line and polygon as inputs. (Chang, 2014)
- 7. Buffering • Proximity analysis : “what’s near what?” • Buffering creates buffer zones by measuring straight-line distances from selected features (points, lines or polygons). • Appropriate and accurate outputs depend on same measurement units Diagrams from webhelp.esri.com
- 8. Buffering • Buffering output : buffer zone (a new feature) represented as a polygon containing the selected feature (source: adapted from http://resources.arcgis.com/en/help/main/10.2/index.html#//000800000019000000 )
- 9. Buffering applications Delimitation of protected zones around features Defining buffer zones along river streams to restrict urban developments Creating restrictions criteria for the location of an industrial site based on buffers along conservation areas, river streams, residential areas, … Definition of areas of influence Generating a buffer zone centred on a school to estimate the number of potential students Creating an inclusion zone for an industrial site using buffers along main roads, logistics centres, industrial city areas,…
- 10. Buffering applications Delimitation of protected zones around features GIS spatial analysis using buffer to identify riparian land use
- 11. Buffering applications Definition of areas of influence GIS spatial analysis using buffer to define a search radius centred in one specific feature
- 12. Overlay • Overlay analysis : “what’s within what?” • Overlay creates an output by combining geometries and attributes from different layers (either vector or raster). • Appropriate and accurate outputs depend on same coordinate system
- 13. Overlay Overlay output: combines two different layers to form a new layer (different geometry and attribute table)
- 14. Overlay operations Union Intersection Union • preserves all features from the input and overlay layers • the area extent of the output combines the area extents of both layers • input layers have to be polygons Intersect • preserves only those features that fall within the area extent common to both layers • inputs can take any geometry but the overlay layer is a polygon • the attribute table contains only data from both layers (source: adapted from http://resources.arcgis.com/en/help/main/10.2/index.html#/Overlay_analysis/018p00000004000000/ )
- 15. Overlay operations Symmetrical difference • preserves features common to either the input layer or overlay layer but not both • the geometry of the overlay layer as to be the same as the input Identity • preserves only features that fall within the area extent of the input layer • the overlay layer has to be a polygon or the same geometry as the input Symmetrical difference Identity (source: adapted from http://resources.arcgis.com/en/help/main/10.2/index.html#/Overlay_analysis/018p00000004000000/ )
- 16. Overlay applications Overlaying watershed boundaries (polygon) with a vegetation layer (polygon) to calculate the amount of each vegetation type in each watershed. Overlay of different layers to find a specific location suitable for a particular use or susceptible to some risk, for example, overlaying layers representing vegetation type, slope, aspect and soil moisture to find areas susceptible to wildfire. Logging roads (lines) and vegetation types (polygons) overlayed to create a new line feature class
- 17. Distance measurement Measure of the Euclidean distance (i.e., in a straight line) between spatial features in a vector layer Proximity analysis: “ How close?”, “What is the distance?” “What is the nearest or farthest feature from something?” Distance from each point in one feature class to the nearest point or line feature in another feature class. Example: find the closest stream for a set of wildlife observations or the closest bus stops to a set of tourist destinations http://resources.esri.com/help/9.3/arcgisengine/java/gp_toolref/geoprocessing/proximity_analysis.htm
- 18. Distance measurement Distance from each point in one feature class to all the points within a given search radius in another feature class. Example: find the distance and direction to all the water wells within a given distance of a test well where you identified a contaminant http://resources.esri.com/help/9.3/arcgisengine/java/gp_toolref/geoprocessing/proximity_analysis.htm
- 20. Spatial analysis using raster The raster data model uses a regular grid to cover the space and the value in each grid cell to represent the characteristic of a spatial phenomenon at the cell location. In contrast with vector data analysis, which uses points, lines and polygons, raster data analysis uses cells and rasters . (Chang, 2014)
- 21. Raster analysis tools Local Neighbourhood Zonal Global One-to-one cell Output value depends on the input value at a cell location and the values of the cells in a specified neighbourhood around that location Output value depends on the value of the cell at the location and the association that location has within a cartographic zone. Input Output Output value function of all the cells combined from the various input raster datasets
- 22. Local operations Local output: new raster where the output cell values are calculated based on the input raster. Each cell on the input raster determines the value of the output cell (in the same location), regardless the values in the neighbourhood cells. Mathematical functions (arithmetic, logarithmic, trigonometric and power functions) are used for local operations. Raster Sum http://help.arcgis.com/en/arcgisdesktop/10.0/help/index.html#/How_Cell_Statistics_works/009z00000088000000/
- 23. Local operations - Reclassification Creates a new raster by assigning new cell values based on their interpretation. Frequently used in GIS projects since it helps simplifying raster data (hence making the results easier to interpret). It is commonly used to assign different categories in a raster.
- 24. Distance measurements Physical distance (Euclidean distance measured from one cell centre to the other) Each output cell has the distance to the nearest river feature Another example: Forest fire model where the distance from a currently burning cell determines next cell burning
- 25. Distance measurements Cost distance (i.e. measuring the cost associated with a physical distance) Calculates the least accumulative cost distance for each cell to the nearest source over a cost surface. Measuring cost distance helps to find the least-cost path: the best route for a new road in terms of construction costs; developing a hiking trail system in a national park; finding cost-effective routes between places on delivery routes, national monuments or other destinations
- 26. Least-cost path http://help.arcgis.com/en/arcgisdesktop/10.0/help/index.html#/Understanding_cost_distance_analysis/009z000000z5000000/ and from http://help.arcgis.com/en/arcgisdesktop/10.0/help/index.html#/Creating_the_least_cost_path/009z00000021000000/ )
- 27. next week SCI103 notes: Go through section 3 - Module 3 in your Learning Modules The information presented here is important for Assessment 4a) and Assessment 5. Start planning Assessment 5 (any questions yet?)