Advanced GIS Using ESRI ArcGIS 9.3 Spatial Analyst 2

Spatial Analyst Cell Statistics A raster will be created depicting the spatial distribution of various statistic parameters calculated for 2 or more input rasters

Spatial Analyst Cell Statistics MAJORITY — Calculates the majority (value that occurs most often) of the inputs. MAXIMUM — Calculates the maximum (largest value) of the inputs. MEAN — Calculates the mean (average) of the inputs. MEDIAN — Calculates the median of the inputs. MINIMUM — Calculates the minimum (smallest value) of the inputs. MINORITY — Calculates the minority (value that occurs least often) of the inputs. RANGE — Calculates the range (difference between largest and smallest value) of the inputs. STD — Calculates the standard deviation of the inputs. SUM — Calculates the sum (total of all values) of the inputs. VARIETY — Calculates the variety (number of unique values) of the inputs.

Spatial Analyst Cell Statistics Example of result

Spatial Analyst Neighborhood Statistics Statistical parameters (the same as for the previous command) can be calculated for a specified neighborhood in a map (point or raster), creating a new raster

Spatial Analyst Neighborhood Statistics The neighborhood can be defined as a rectangle (rarely used), giving its size

Spatial Analyst Neighborhood Statistics The neighborhood can be defined as a rectangle (most used), giving its radius

Spatial Analyst Neighborhood Statistics The neighborhood can be defined as an annulus (similar to a circle with low- pass filter), giving its radiuses

Spatial Analyst Neighborhood Statistics The neighborhood can be defined as a wedge (useful in case of spatial trends and/or to highlight them), giving its radius and its starting and ending directions

Spatial Analyst Zonal Statistics Calculates a table of statistics (Mean, Majority, Maximum, Median, Minimum, Minority, Range, Standard Deviation, Sum or Variety) on values of a raster within the zones of another dataset. An histogram can be created too for one of the statistic parameters.

Spatial Analyst Zonal Statistics Result

Spatial Analyst Zonal Histogram Draws a chart of the frequency of valus in a raster map divided by zones defined by a shapefile (generally polygons)

Spatial Analyst Zonal Histogram Result

Spatial Analyst Reclassify Reclassifies a raster Classes are defined by thresholds, either manually typed or created with the classify option (identical to that used for symbology)

Spatial Analyst Reclassify Result

Spatial Analyst Convert Feature to Raster Creates a raster whose cell will contain a value/label derived from a field of a shapefile. It will cause loss of accuracy (frequently also errors)

Spatial Analyst Convert Feature to Raster Points

Spatial Analyst Convert Feature to Raster Points Result

Spatial Analyst Convert Feature to Raster Points Problems All the values are shifted to the center of their cell Value shifted

Spatial Analyst Convert Feature to Raster Points Problems Since each cell can contain only one vaue, when two source points are located in the same cell one of them will be lost Value lost

Spatial Analyst Convert Feature to Raster Lines

Spatial Analyst Convert Feature to Raster Lines Result

Spatial Analyst Convert Feature to Raster LInes Problems Reshaping/ simplification of lines “Widening” of lines

Spatial Analyst Convert Feature to Raster Points Problems Since each cell can contain only one vaue, when two or more source lines cross the same cell only the attribute of one of them will be preserved Value lost

Spatial Analyst Convert Feature to Raster Polygons

Spatial Analyst Convert Feature to Raster Polygons Result

Spatial Analyst Convert Feature to Raster Polygons Problems Reshaping/ simplification of polygons Very small polygons can be lost

Spatial Analyst Convert Raster to features Also the conversion of rasters to features will generate errors

Spatial Analyst Convert Raster to features to points A shapefile of points will be created containing one point for each (non empty) cell of the source raster

Spatial Analyst Convert Raster to features to points Result

Spatial Analyst Convert Raster to features to points

Spatial Analyst Convert Raster to features to points Result

Spatial Analyst Convert Raster to features to points

Spatial Analyst Convert Raster to features to points Result

Spatial Analyst Convert Raster to features to points Problems

Spatial Analyst Convert Raster to features to Lines A shapefile of Polylines will be created containing lines following the boundaries between cells containing different values

Spatial Analyst Convert Raster to features to points Result Completely unuseful

Spatial Analyst Convert Raster to features to Lines

Spatial Analyst Convert Raster to features to Lines Result

Spatial Analyst Convert Raster to features to Lines Result Problems

Spatial Analyst Convert Raster to features to lines A raster created from points generally is not accepted to generate polylines or polygons

Spatial Analyst Convert Raster to features to Polygons A shapefile of Polygons will be created following the boundaries between cells containing different values

Spatial Analyst Convert Raster to features to Polygons Result

Spatial Analyst Convert Raster to features to Polygons Result Problems

Spatial Analyst Convert Raster to features to Lines

Spatial Analyst Convert Raster to features to Lines Result Practically unuseful

Spatial Analyst Raster Calculator The Raster Calculator can perform mathematical calculations using operators and functions, set up selection queries, or type in Map Algebra syntax. Inputs can be raster datasets (or raster layers, coverages, shapefiles, tables, constants, and numbers).

Spatial Analyst Raster Calculator The most common functions are represented by icons on the right; further function are available cliching on the “expand” button (bottom right)

Spatial Analyst Raster Calculator Expressions can be simply typed or created using the selection fields and the function icons. Clicking the “Evaluate” button a new raster will be created containing the result For example, the spatial distribution of the average number of components of families can be avaluated simply dividing the raster containing the interpolated value of inhabitants per municipality by that created interpolating the number of families per municipality

Spatial Analyst Raster Calculator Result The resulting map is always a remporary raster called “Calculation” (if needed adding a number) that can be saved into the HD

Spatial Analyst Raster Calculator Result Extent and cell size of the resulting map are to be set in the “Options” sector of the Spatial Analyst Menu