Spatial Analysis with Raster Datasets - 2

Francisco Olivera, Ph.D., P.E.Srikanth Koka

Department of Civil EngineeringTexas A&M University

Reclassification

Reclassify creates a new grid by replacing the input cell values with new output cell values.

New cell values are based on new information or grouping existing values together.

To reclassify, click on Spatial Analyst/Reclassify.

Straight Line Distance

Straight Line gives the distance from each cell in the grid to the closest source (point or line dataset).

Optionally, Create Allocation and Create Direction can be used to create grids with cells representing the value of the source and direction (out of eight options) of the source, respectively.

To use the straight line distance function, click on Spatial Analyst/ Distance/Straight Line.

Allocation

Allocation is used to allocate cells to the closest source. The source can be a point feature class or any grid or feature class. It is similar to the Straight Line Allocation function.

To create an allocation grid click on Spatial Analyst/ Distance/Allocation.

Cost Weighted Distance

The Cost Weighted Distance function creates a grid in which each cell represents the least accumulative cost from that cell to the nearest, cheapest source (cost can be money, time, etc.).

Needs a cost grid; for example: Cost raster = f(slope, landuse).

To create a cost weighted distance grid, click on Spatial Analyst/Distance/Cost Weighted.

Calculation = 0.34*Reclass of landUse + 0.66* Reclass of Slope

DensityDensity can be used to create a continuous density surface from a set of input features within the search area.

The options for creating a density grid are Simple density or Kernel density.

To create a density surface, click on Spatial Analyst/Density. Density surface of population

data

Interpolate to RasterInterpolate to raster is a global function which creates a grid that stores values interpolated from a point feature dataset.

The options are Inverse Distance Weighted, Spline and Kriging.

To create an interpolated surface, click on Spatial Analyst/Interpolate to Raster.

Surface Analysis-Contour

Create contours creates a line feature dataset in which the lines connect points of equal cell value.

To create contours, click on Spatial Analyst/Surface Analysis/Contour.

Surface Analysis-Slope

Slope is a neighborhood function which creates a grid of maximum rate of change of the cell values of the input grid. The slope is derived based on a 3 x 3–cell neighborhood.

Slope does not indicate the direction of the calculated slope.

To create a slope surface, click on Spatial Analyst/Surface Analysis/Slope.

Surface Analysis-Aspect

Aspect is a neighborhood function which creates a grid of aspect or direction of maximum slope of the cells of the input grid.

Aspect values are in degrees with 0° for the North direction.

To create a aspect surface, click on Spatial Analyst/ Surface Analysis/Aspect.

Surface Analysis-Hillshade

Hillshade is a neighborhood function which creates a grid of surface brightness for a given position of a light source.

Hillshade values can be used to enhance the legend of themes.

To create a hillshade surface, click on Spatial Analyst/Surface Analysis/ Hillshade.

Surface Analysis-Viewshed

Viewshed is a global function which creates a grid of visible and non-visible surface from an observation point.

To create a viewshed grid, click on Spatial Analyst/ Surface Analysis/ Viewshed.

Surface Analysis-Cut/FillCut/Fill is a local function that creates a surface with cells representing the area and volume of cut or fill needed to modify a source surface to a destination surface.

To create a cut/fill surface, click on Spatial Analyst/Surface Analysis/Cut/Fill.

Only in ArcGIS 8.3

Cell StatisticsCell Statistics is a local function that creates a grid with cell values equal to a statistic of the corresponding cell values of the input grids.

The statistic can be: majority, maximum, mean, median, minimum, minority, range, standard deviation, sum and variety.

To calculate the statistics of a set of grids, click Spatial Analyst/Cell Statistics…

Neighborhood Statistics is a focal function that creates a grid with cell values equal to a statistic of the neighborhood cell values of the input grid.

The statistic can be: majority, maximum, mean, median, minimum, minority, range, standard deviation, sum and variety.

The neighborhood can have different shapes.

To calculate neighborhood statistics, select the grid and click on Spatial Analyst/Neighborhood Statistics…

Neighborhood Statistics

Mean over a 5-cell-radius circular neighborhood

Zonal StatisticsZonal Statistics is a zonal function that creates a table with all the statistics of the cell values within each zone. Table rows correspond to zones and columns to statistics. This function can also create a chart of user-specified statistics.

The statistics are: majority, maximum, mean, median, minimum, minority, range, standard deviation, sum and variety.

The zones can be defined by polygons or (integer) grid cells with the same value.

To summarize by zones, click on Spatial Analyst/Zonal Statistics…

Raster Calculator

The Raster Calculator is a calculator that evaluates local functions.

To query grids, click on Spatial Analyst/Raster Calculator…

DEM < 100

Histogram

The Histogram is a global function that creates a column chart of the cell values.

To create a histogram, click on the Histogram tool.

Histogram of cell values of the reclassification of elevation grid

into 10 classes