Raster Analysis I Overview

1. GEO4152 Applications in GIS Raster Analysis I Overview • Grid layers • Setting grid layer and analysis properties • Grid function types • Performing grid analysis • Map Algebra

2. Overview • Grid layers • Setting grid layer and analysis properties • Grid function types • Performing grid analysis • Map Algebra

3. Grid layers: Overview • Grid layer • Grid layer properties • Examining cell values in grid layers • Managing grid layer files

4. Grid layers: Overview • Grid layers are ArcGIS's implementation of the basic raster data model.

5. Grid layers: Overview • Grid layers are ArcGIS's implementation of the basic raster data model. rectangular tessellation of square cells

6. Grid layers: Overview • Grid layers cellshave numerical value

7. Grid layers: Overview • Grid layers are suited for representation of phenomena that vary gradually over space such as elevation, wind speed and direction, or slope.

8. integer (no decimals) floating-point(decimals) Grid layers: Grid types • Only integer grids can have layer tables

9. Grid layers: Grid types • Only integer grids can have layer tables

10. Grid layers: The spatial analyst • All grid layer functionality occurs through the Spatial Analyst extension.

11. Grid layers: Grid layer properties • Layer description contains a lot of information

12. Grid layers: Grid layer properties • Layer description contains a lot of information

13. Grid layers: Grid layer properties • Layer description contains a lot of information

14. Y-axis: cellcounts X-axis: values Grid layers: Examining cell values with histogram • Histograms describe structure of data values

15. Grid layers: Examining cell values with identify tool • Individual cell values can be identified

16. Grid layers: Managing grid layer data files • Grid data sources can be managed by ArcCatalog • copying • moving • renaming • deleting

17. Overview • Grid layers • Setting grid layer and analysis properties • Grid function types • Performing grid analysis • Map Algebra

18. Setting grid analysis properties • Analysis properties • Working directory • Masking • Spatial extent of output • Cell size • Once set, analysis property values stay set until changed Analysis properties determine spatial properties for all newly created output grid layers

19. Setting grid analysis properties: Analysis extent • Analysis extent sets the spatial properties for output of analyses • Rectangular area

20. Setting grid analysis properties: Analysis extent • Be careful about setting extent; it may cause poor grid-to-grid registration

21. Setting grid analysis properties: Cell size • Analysis cell size sets the grid cell size for output of analyses • use consistent cell size for analysis of multiplegrid data sets • small cells → larger files • small cells → longer processing

22. Setting grid analysis properties: Masking • Analysis mask defines spatial extent of output grids • Mask is the “valid data” area of an existing gridrather than a rectangularregion (as in AnalysisExtent)

23. Setting grid analysis properties: Masking • Analysis mask defines spatial extent of output grids

24. Overview • Grid layers • Setting grid layer and analysis properties • Grid function types • Performing grid analysis • Map Algebra

25. Overview • Grid layers • Setting grid layer and analysis properties • Grid function types • Performing grid analysis • Map Algebra

26. Grid function types • Local • Global functions • Zonal functions • Focal functions

27. local sine e.g. sin(12) = -0.537 Grid function types: Global functions • Local functions apply an independent calculation to only one input grid cell for each output cell.

28. Grid function types: Global functions • Global functions apply a calculation based on all cell values e.g. flow accumulation

29. Grid function types: Zonal functions • Zonal functions apply one calculation to all input grid cells within each zone zonal sum for zone 1: (53 + 57 + 33 + 78 + 31 + 12 + 32 + 9 + 9 + 33 + 76) = 423

30. focal mean Grid function types: Focal functions • Focal functions apply one calculation to all input grid cells within a “focus” (27 + 8 + 22 + 16 + 21 + 16 + 6 + 44 + 8) / 9  18.7

31. Overview • Grid layers • Setting grid layer and analysis properties • Grid function types • Performing grid analysis • Map Algebra

32. Grid analysis: calculations across multiple grids • Multi-grid analyses are possible because of spatial registration • multiple grid layers share the same X, Y coordinate space • cell values are calculated across multiple grid layers • to create a single output grid layer

33. Grid analysis • Analyses are performed using GUI tools (1) Spatial Analyst toolbar (2) Raster Calculator

34. Grid analysis • Analyses are performed using GUI tools (3) ArcToolbox

35. Grid analysis • Many more grid analyses are available through the Grid Map Algebra syntax

36. Overview • Grid layers • Setting grid layer and analysis properties • Projections and grid layers • Grid function types • Performing grid analysis • Map Algebra

37. Grid layers may be used in arithmetic expressions output_data_set = input_grid1 operator input_grid2 . . . slp_dem = slp_grid * dem Grid layers may be used in algebraic functions output_data_set = function (input_data_set[s] {,arguments}) slp_grid = slope (dem, percentrise) Grid analysis: Map algebra

38. operator classes operators raster layers expressionbox Performing grid analysis: Using grids in math • Map algebra is calculated with the Raster Calculator

39. Grid analysis: Map algebra ( “How it works”) • Map Algebra arithmetic: Calculation = (Dem gt 500 and Dem lt 1000 ) Logical (Boolean) criteria

40. 0 = false 1 = true Grid analysis: Map algebra ( “How it works”) • Map Algebra arithmetic:

41. Grid analysis: Map algebra (“How it works”) • Map Algebra function: Map Calculation 1 = mosaic({Elbe, Eaton}) Mosaics the Elbe and Eaton grids

42. Grid analysis: Map algebra ( “How it works”) • Map Algebra function: