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

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 ofsquare cells

6 Grid layers: Overview Grid layers cells have 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 Grid layers: Grid types Only integer grids can have layer tables floating-point (decimals) integer (no decimals)

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 Grid layers: Examining cell values with histogram Histograms describe structure of data values Y-axis: cell counts X-axis: 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 multiple grid 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 grid rather than a rectangular region (as in Analysis Extent)

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

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 for zone 1: ( ) = 423 zonal sum

30 Grid function types: Focal functions Focal functions apply one calculation to all input grid cells within a “focus” focal mean ( ) / 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 analysis: Map algebra 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)

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

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

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

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: