Lab 1 Flashcards
What’s the difference between calculating statistics between raster (local, per-cell analysis), within neighborhoods, and within zones?
Difference between local, neighborhood, and zonal:
a. The local tools are those where the value at each cell location on the
output raster is a function of the values from all the inputs at that location.
b. Neighborhood tools create output values for each cell location based on
the location value and the values identified in a specified neighborhood.
The neighborhood can be of two types: moving or search radius.
c. The Zonal tools allow you to perform analysis where the output is a result
of computations performed on all cells that belong to each input zone. A
zone can be defined as being one single area of a particular value, but it can also be composed of multiple disconnected elements, or regions, all
having the same value. Zones can be defined by raster or feature
datasets. Rasters must be of integer type, and features must have an
integer or string attribute field.
What is a raster?
A spatial data model that defines space as an array of equally sized cells, arranged in rows and columns, and composed of single or multiple bands (layers). Each cell contains an attribute value. Unlike a vector structure, which stores coordinates explicitly, raster coordinates are inherently contained in the ordering of the matrix. Groups of cells that share the same value represent the same type of geographic feature.
What is a cell?
A cell is the smallest unit of information in raster data. Each cell represents the numeric value of some measure at the corresponding unit area location on the earth.
What is the most common way to access Spatial Analyst functionality?
With the geoprocessing tools
What are three ways to perform Spatial Analyst operations?
- Running individual tool dialogs
- combine tools with Model builder
- Automate work flows and create new tools with Pyton.
How do you enable the Spatial Analyst extension?
To enable an extension, select Extensions from the Customize menu in ArcMap,
ArcCatalog, ArcGlobe, or ArcScene (the application that comes with the ArcGIS
3D Analyst extension).
What are the shape of raster cells?
Square
It is important to note that Spatial Analyst performs operations on square cells
only. Thus, the size of each cell, known as its resolution, must be the same in
each dimension.
Describe some of the various functionality available in the Surface toolset of the Spatial
Analyst extension.
With these tools, you can derive new information about a surface dataset. For
each location, you can determine the angle of the surface (slope), the steepest
downslope direction (aspect), or the second derivative of the surface (curvature).
You can also generate a line dataset that connects locations of equal value
(contours), create a shaded relief, calculate the volume changes between two
surfaces, and determine the visibility of locations.
Describe the two interactive tools available in the Spatial Analyst toolbar.
There are two interactive tools you can use on the Spatial Analyst toolbar.
a. The Create Contour interactive tool enables you to create individual
contours (lines that connect cells of equal value) at specific locations on a
single-band raster. You might want to identify locations at the same
elevation, with the same temperature, or with the same atmospheric
pressure.
b. The Histogram interactive tool enables you to explore the distribution of
values in a raster layer. For example, you might want to know the number
of cells (the count) with a certain value, such as the number of cells that
are forested land or vacant property.
What is map algebra?
Map Algebra is a simple and powerful algebra with which you can execute all
Spatial Analyst tools, operators, and functions to perform geographic analysis.
What are three ways to use Map Algebra?
- the Raster Calculator tool
- The Python window
- Your favourite Python integrated development environment (IDE)
