1. Copyright © 2006 by Maribeth H. Price 15-1 Chapter 15 Raster Analysis

2. Copyright © 2006 by Maribeth H. Price 15-2 Outline About rasters The grid raster format Raster analysis basics –Map algebra –Boolean overlay –Other raster functions Using Spatial Analyst

3. Copyright © 2006 by Maribeth H. Price 15-3 Outline Differences between the raster and vector data models and the benefits and drawbacks of each Basic facts about the storage and use of the grid data model Getting familiar with basic raster analysis functions Using Boolean map algebra to perform overlay analysis with rasters Controlling the analysis environment when using Spatial Analyst Using Spatial Analyst for raster analysis

4. Copyright © 2006 by Maribeth H. Price 15-4 The raster data model Rows Columns X, Y location Raster data file N rows by M columns X, Y location Georeferenced to earth’s surface

5. Copyright © 2006 by Maribeth H. Price 15-5 Types of raster data Discrete raster: land use Continuous raster: DEM Continuous raster: image Discrete raster: roads

6. Copyright © 2006 by Maribeth H. Price 15-6 Raster Properties Scroll down for more info

7. Copyright © 2006 by Maribeth H. Price 15-7 Raster vs Vector models Raster strengths –Simple, robust format –Implicit georeferencing –Storage of continuous data –Surface analysis –Faster analysis Raster drawbacks –Storage space –Lower precision Vector strengths –Coordinate precision –Attribute management –Storage space –Flexible cartography Vector weaknesses –Surface analysis –Continuous data storage “Raster is faster, but vector is correcter.”

8. Copyright © 2006 by Maribeth H. Price 15-8 Raster resolution Measured by cell size Storage space increases dramatically with precision Vector format200 m raster50 m raster

9. Copyright © 2006 by Maribeth H. Price 15-9 Raster formats Grids –Special format for Spatial Analyst –Required to perform analysis –Integer or floating-point values Other formats –JPEG, TIFFs, MrSID, etc. –For display only

10. Copyright © 2006 by Maribeth H. Price 15-10 Naming grids Names must be 13 characters or less Do not use spaces or non-alphanumeric characters to name grids No spaces in folders or grids –(underscore is OK) Remember. No spaces.

11. Copyright © 2006 by Maribeth H. Price 15-11 Managing grids Working directories tend to get clogged with grids after a while and will need to be cleaned out Grids have complex data format Copy, move, and delete grids ONLY with ArcCatalog!!!!

12. Copyright © 2006 by Maribeth H. Price 15-12 Grid attribute tables Created for discrete integer grids only Geology

13. Copyright © 2006 by Maribeth H. Price 15-13 Converting features to raster Choose one attribute Grid value Text attribute carried over

14. Copyright © 2006 by Maribeth H. Price 15-14 Converting raster to features Convert only discrete data without too many polygons To complex to convert OK to convert

15. Copyright © 2006 by Maribeth H. Price 15-15 NoData Specific grid value to indicate lack of data Often replaced by zero in other formats Used to create masks NoData

16. Copyright © 2006 by Maribeth H. Price 15-16 Georeferencing rasters Rows Columns x,y location Raster data file N rows by M columns x,y location Georeferenced to earth’s surface

17. Copyright © 2006 by Maribeth H. Price 15-17 Georeferencing of images Some raster data comes already georeferenced, with an assigned coordinate system. –Landsat image –Digital elevation models –Digital map products from the USGS Other rasters have no georeferencing and must be prepared before use –Scanned maps or photos, pictures grabbed from Web

18. Copyright © 2006 by Maribeth H. Price 15-18 The Georeferencing toolbar is used to link image locations to corresponding locations in an already georeferenced data set. After the links are established a final georeferenced map can be produced.

19. Copyright © 2006 by Maribeth H. Price 15-19 Raster analysis Basic concepts Map Algebra Boolean overlay

20. Copyright © 2006 by Maribeth H. Price 15-20 Map Algebra Rasters are essentially arrays of numbers Can be added, subtracted, etc Line up matching cells vertically 5 7 2 4 3 2 1 6 8 9 3 10 Ingrid1 + Ingrid2 = Outgrid Fig. 15.4. Map algebra

21. Copyright © 2006 by Maribeth H. Price 15-21 Map Algebra expressions Convert precipitation in cm to inches – [Precip] / 2.54 Compute earth volume to be moved – [InitialSurface] – [Finalsurface] Enter models based on multiple inputs [Precip] * 2 + [Slope] * 4 / ( [Erode] – [Vegcover] Logical expressions –[Elevation > 1400]

22. Copyright © 2006 by Maribeth H. Price 15-22 Conversions [Precip_cm] / 2.54 Precip in cmPrecip in inches

23. Copyright © 2006 by Maribeth H. Price 15-23 Cut and fill on a site [Initial surface] – [final surface] Cut Fill

24. Copyright © 2006 by Maribeth H. Price 15-24 Model expressions Complex expressions with multiple inputs to calcuate risk or hazard index. Runoff in cm based on four input grids: precip, slope, soil infiltration, and vegetation cover. [Precip] * 2 + [Slope] * 4 / ( [Erode] – [Vegcover]

25. Copyright © 2006 by Maribeth H. Price 15-25 Logical expressions Produce a Boolean grid of 1’s and 0’s –1 = True –0 = False [EarthMove] > 0 1 0 Elevation > 1400 1 0

26. Copyright © 2006 by Maribeth H. Price 15-26 Boolean expressions A AND B A XOR BA NOT B A OR B A B 0 1 Blue circles represent areas where condition holds (True) = 1

27. Copyright © 2006 by Maribeth H. Price 15-27 Boolean Map Algebra True (1) False (0) A AND BA OR BA NOT BA XOR B Inputs ABAB Output Compare values of corresponding cells and determine output value

28. Copyright © 2006 by Maribeth H. Price 15-28 Boolean overlay using map algebra 0 1 0 1 0 1 AND = Find intersecting areas where all conditions are true to determine lodgepole habitat. Equivalent of vector Intersect

29. Copyright © 2006 by Maribeth H. Price 15-29 Another way to look at Boolean intersection 0 1 0 1 0 1 x = Boolean AND is equivalent to multiplication. So multiplying layers works just as well. 1 AND 1 = 1 1 AND 0 = 0 0 AND 1 = 0 0 AND 0 = 0 1 × 1 = 1 1 × 0 = 0 0 × 1 = 0 0 × 0 = 0

30. Copyright © 2006 by Maribeth H. Price 15-30 Additive Boolean overlay 0 1 2 0 1 0 1 + = Instead of multiplying, add the layers together to create a ranked probability result.

31. Copyright © 2006 by Maribeth H. Price 15-31 Other raster analysis techniques Reclassification Surface functions Distance functions Density functions Interpolation Neighborhood functions Zonal functions

32. Copyright © 2006 by Maribeth H. Price 15-32 Reclassify Convert one set of grid values to another Manual or classify SlopeHigh slope/low slope

33. Copyright © 2006 by Maribeth H. Price 15-33 Surface analysis DEM Slope Aspect Hillshade Contouring

34. Copyright © 2006 by Maribeth H. Price 15-34 Viewshed analysis Areas visible from a set of observation points

35. Copyright © 2006 by Maribeth H. Price 15-35 Distance functions Straight line distance Cost path distance Buffers

36. Copyright © 2006 by Maribeth H. Price 15-36 Lowest cost path 1. Create start/stop shapefiles 2.Create cost grid 3.Calculate cost distance grid and cost direction grid 4.Find lowest cost path ElevationSlope Cost distanceCost direction

37. Copyright © 2006 by Maribeth H. Price 15-37 Density Calculate from point distributions

38. Copyright © 2006 by Maribeth H. Price 15-38 Interpolation Estimate gridded values between known points Three options –Inverse distance weighted –Kriging –Splining Rainfall grid from weather station data

39. Copyright © 2006 by Maribeth H. Price 15-39 Neighborhood functions Output gridInput grid 314 621 5 43 314 4 1 3 4 3144 1 2 4 1 1 2.02.53.42.83.6 3.83.22.93.02.3 3.13.32.5 Window Target cell Averaging function

40. Copyright © 2006 by Maribeth H. Price 15-40 Neighborhood majority High slope/low slope areas Before 5x5 majority filterAfter two passes of 5x5 majority filter Useful for simplifying rasters prior to conversion to polygons

41. Copyright © 2006 by Maribeth H. Price 15-41 Cell statistics Calculate statistics for a stack of grids

42. Copyright © 2006 by Maribeth H. Price 15-42 Zonal statistics Zones defined by a layer Value grid Calculates value statistics for each zone Watersheds Average slope

43. Copyright © 2006 by Maribeth H. Price 15-43 Using Spatial Analyst Executing functions Temporary vs permanent output grids Resampling and coordinate systems Analysis environment options –Workspace –Extent –Cell size –Masks

44. Copyright © 2006 by Maribeth H. Price 15-44 Menu tools Most commonly used functions are in the Spatial Analyst toolbar More functions can be found in ArcToolbox Some tools are slightly different than the menu tool—may have more or different options

45. Copyright © 2006 by Maribeth H. Price 15-45 ArcToolbox Hundreds of additional functions found in ArcToolbox Use them in scripts and models if desired Spatial Analyst is an incredibly powerful raster processing package

46. Copyright © 2006 by Maribeth H. Price 15-46 Raster Calculator Use for executing map algebra expressions Use to access Toolbox functions by directly typing tool command and arguments into the calculator.

47. Copyright © 2006 by Maribeth H. Price 15-47 ModelBuilder Use Spatial Analyst tools in ModelBuilder just as you can use any other tools. This model generates watersheds and streams from a digital elevation model (DEM) using the Spatial Analyst hydrologic functions.

48. Copyright © 2006 by Maribeth H. Price 15-48 Analysis output types Permanent grids –Given name and location at time of creation –Can be used by other map documents Temporary grids –Created in working directory* –Rename in map document once created –May be converted to permanent grids later –Deleted from disk when removed from map! *Set location where grids are created by default

49. Copyright © 2006 by Maribeth H. Price 15-49 Output coordinate systems Grids best stored in projected coordinate system for analysis Coordinate systems will be resampled or reprojected on the fly during analysis if needed –Convenient, but time-consuming Coordinate system handling –Output matches first raster input –Vectors will be reprojected to match rasters –User can override defaults by specifying that all raster output will be in data frame coordinate system

50. Copyright © 2006 by Maribeth H. Price 15-50 The analysis environment General options –Working directory –Mask grid –Coordinate system options Analysis extent Analysis cell size

51. Copyright © 2006 by Maribeth H. Price 15-51 General options Working directory Analysis mask Analysis coordinate system

52. Copyright © 2006 by Maribeth H. Price 15-52 Analysis mask Mask grid Elevation after masking NoData Data Applies to ALL output grids Masks may be grids, polygon shapefiles or feature classes. Coverages may not work properly.

53. Copyright © 2006 by Maribeth H. Price 15-53 Clipping a grid with masks [Elevation] mask “Clip” grid by using Raster Calculator with a mask. Specify the output grid is the same as the input grid.

54. Copyright © 2006 by Maribeth H. Price 15-54 Clipping a grid with the toolbox

55. Copyright © 2006 by Maribeth H. Price 15-55 Analysis extent

56. Copyright © 2006 by Maribeth H. Price 15-56 Cell size and extent Analysis extent Analysis cell size

57. Copyright © 2006 by Maribeth H. Price 15-57 Options/Environments The Spatial Analyst options set in the menu take precedence over the Environment Settings for functions executed from the menus. Tools, however, will honor the environment settings instead of the options settings

58. Copyright © 2006 by Maribeth H. Price 15-58 Did I mention not to use spaces in folder names?