1. Review- vector analyses
Selection
Topological Overlays
Buffering

2. Selection Selecting points near a line (proximity)
Selecting adjacent features (proximity)
Selecting lines within polygons (containment)
Selecting polygons that contain lines (overlap)
Selecting points within polygons (containment)
Selecting polygons that contain points (overlap)
Selecting polygons that overlap polygons (overlap)

3. Types of overlays
Union
Clip
Identity
Intersect
Update
Erase

4. Clipping… an example

5. Clipping… an example

6. ArcGIS does NOT automatically update geometry fields for shapefiles

7. Raster Analysis

8. Overview Grid layers Setting grid layer and analysis properties
Grid function types
Performing grid analysis
Map Algebra
More grid analyses

9. Grid layers

10. Grid layers
The grid layer is the format ArcInfo uses for raster data.

11. Grid layers
A grid layer is a rectangular grid of square cells

12. Grid layers
Not all raster datasets are grid layers
reflectance
values

13. Grid layers
Cells have numeric values

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

15. Grid types
integer (no decimals)
floating-point (decimals)

16. Grid types
Integer grids can have value attribute tables (VATs), floating point grids do NOT

17. Grid types Integer grids with: a range of values < 100,000
and < 500 unique values
will have attribute tables

18. Displaying grid layers
Legends can be altered like other layers

19. Identity tool
Individual cell values can be identified

20. Queries
Integer grids can be queried in the same way as vector layers (select by attribute)

21. Setting grid layer and analysis properties

22. Setting 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

23. Analysis extent
Analysis extent sets the spatial properties for output of analyses
Rectangular area

24. Analysis extent
Be careful about setting extent; it may cause poor grid-to-grid registration

25. Cell size
Analysis cell size sets the grid cell size for output of analyses
Use a consistent cell size for analysis of multiple grid data sets
small cells → larger files
small cells → longer processing

26. Masking Analysis mask defines spatial extent of output grids
Mask can be any shape (as opposed to the Analysis Extent)

27. Grid function types

28. Grid function types Local Global functions Zonal functions
Focal functions

29. Local functions
Local functions apply an independent calculation to all input grid cells
local sine
e.g. sin(12) =

30. Global functions
Global functions apply a calculation based on all cell values
e.g. flow accumulation

31. Zonal functions
Zonal functions apply one calculation to all input grid cells within each zone
Zones are defined as a group of cells having the same value
Regions are groups of contiguous cells having the same value

32. Zonal functions
Zonal functions apply one calculation to all input grid cells within each zone
zonal sum
for zone 1:
( ) = 423

33. Focal functions
Focal functions apply one calculation to all input grid cells within a focal distance
focal mean
( ) / 9  18.7

34. Performing grid analysis

35. 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

36. Grid analysis Spatial Analyst toolbar ArcToolbox tools Scripting
Command Line

37. Spatial Analyst toolbar
Raster calculator

38. Spatial Analyst extension

39. Map Algebra

40. Grid analysis: Map algebra
arithmetic expressions
output_data_set = input_grid1 operator input_grid
slp_dem = slp_grid * dem
algebraic functions
output_data_set = function (input_data_set[s] {,arguments})
slp_grid = slope (dem, percentrise)

41. Map algebra can be calculated with the Raster Calculator
operator classes
operators
raster layers
expression box

42. Grid analysis: Map algebra
Map Algebra arithmetic:
Calculation = (Dem gt 500 and Dem lt 1000 )
Logical (Boolean) criteria

43. Grid analysis: Map algebra
0 = false
1 = true

44. More grid analysis
Calculating summary attributes for polygon features using a grid layer (“Zonal Statistics”)
Cross tabulating areas
"Querying" across multiple grid layers
Calculating neighborhood statistics
Calculating distance surfaces and buffers
Determining proximity
Converting raster and vector data sources

45. Calculating summary attributes for polygon features using a grid layer
(“Zonal statistics”)

46. Summarizing zones
Summarizes groups of cells based on integer cells or polygons with similar value
Creates statistical summary of zone
Summary table
Summary chart

47. Summarizing zones

48. Summarizing zones select polygon field to define zones of cells
select grid layer containing variable to summarize
select statistic to graph
specify output

49. statistics from input grid based on polygon zones

50. Ecological Applications: Vol. 17, No. 1, pp. 18–33.
INFLUENCE OF ENVIRONMENT, DISTURBANCE, AND OWNERSHIP ON FOREST VEGETATION OF COASTAL OREGON
Janet L. Ohmann, Matthew J. Gregory, and Thomas A. Spies

52. Cross tabulating areas

53. Cross tabulating areas
Creates a “zonal intersection” of integer grid layers or grids and polygon vectors (similar to vector intersection)
Output is a table
1st input layer creates records (1 record for each unique value)
2nd input layer creates fields (1 field for each unique value)
Table values are map unit area measurements of combinations of zones

54. Cross tabulating areas
Cross-tabulation setup
rows
columns

55. Cross tabulating areas
Output table
record layer (stands)
area measurements in map units
row layer (soils)

56. Cross tabulating areas
Identifying fields

57. Cross tabulating areas

58. Cross tabulating areas

59. "Querying" across multiple grid layers (“Map Query”)
Raster Calculator is easy to use and gives rapid results
Multiple grids can be simultaneously queried (vector overlay only allows 2)
Output represents cells that meet and do not meet query criteria (T or F)

60. "Querying" across multiple grid layers

61. Building Map Queries

63. Calculating neighborhood statistics

64. Calculating neighborhood statistics
Minimum
Maximum
Mean
Median
Sum
Range
Standard Deviation
Majority
Minority
Variety
“Focal” statistical functions
Moving window calculates statistics based on all within the window
Output value is written to central cell in output grid
Statistical functions:

65. Focal Standard Deviation
locations of greatest variation in elevation

66. Calculating distance surfaces and buffers

67. Calculating distance surfaces and buffers
Similar to buffering with vector data
Creates a continuous distance surface rather than a discrete bounded polygonal area
Distance measured from input layer features or grid cells

68. Distance from vector features
continuous distance value surface

69. Create a “graded” buffer by setting a max distance

70. Determining proximity

71. Assigning proximity
Defining territories based on proximity

72. Assigning proximity
output cells have the value of the closest input feature
output value is selected from input layer table
“Thiessen,” “Voronoi”

73. Converting raster and vector data sources

74. Converting raster and vector data sources
Raster  vector conversions are possible
Always a loss or generalization of shape
Support for line, polygon  grid in ArcGIS
Avoid converting grids that do not have large contiguous zones (e.g., DEMs)

75. homework
Read “Raster Analysis 2” & “Data Conversion” & “Model building”
Finish assignment 5
Start assignment 6

76. Ecological Applications: Vol. 17, No. 1, pp. 18–33.
INFLUENCE OF ENVIRONMENT, DISTURBANCE, AND OWNERSHIP ON FOREST VEGETATION OF COASTAL OREGON
Janet L. Ohmann, Matthew J. Gregory, and Thomas A. Spies