__RASTER DATA ANALYSIS__- Raster data analysis is based on cells and rasters
- Raster data analysis can be performed at the level of individual cells, or a group of cells, or cells within an entire raster
- The type of cell value is an important aspect of raster data analysis
- Various types of data are stored in raster format
- Raster data analysis is software specific-raster data. Hence in order to use Digital Elevation Models(DEMs), Satellite images and other raster data in data analysis, they must first be processed and imported to software-specific raster data
- The
**core of raster data analysis**comprises of**local operations**that are cell-by-cell operations. - A local operation can create new raster from a single input raster or multiple input raster.
- Converting a floating point raster to an integer raster is a simple local operation
- Converting a slope raster measured in percent to one measured in degrees is also a local operation
**Reclassification**is a**local operation**that creates a new raster by classification. Reclassification is also called as**recoding or transforming**- Local operations with multiple rasters are also known as
**compositing, overlaying**or**superimposing maps** **Map algebra**is defined as local operations with multiple input rasters.- Local operations compute an output raster dataset where the output value at each location is a function of the value associated with that location on one or more raster datasets
**Focal or Neighbourhood functions**produce an output raster dataset in which output value at each location is a function of the value at a location and the value of cells in a specified neighbourhood around that location**Zonal functions**compute an output raster dataset where the output value for each location depends on the value of the cell at the location and the association that the location has within a cartographic zone.- Global functions compute an output raster dataset in which the output value at each cell location is potentially a function of all the cells in the input raster datasets.
- The two types of global functions are:
- Euclidian distance and
- Weighted distance
- The raster calculator provides powerful tools in algebra syntax to perform mathematical calculations using operators and functions. It can also be used to set-up selection queries or type spatial analyst function syntax. Inputs can be grid datasets or raster layers, shape files, coverages, tables, constants and numbers.
- The raster calculator provides four groups of mathematical functions: Logarithmic, Arithmetic, Trigonometric and Exponential.
- The raster calculator allows boolean, relational and arithmetic operators
- Raster data analysis also involves:
- Terrain analysis
- Contour
- Slope
- Aspect
- Hillshade
- Viewshed
- Cut/Fill
- Hydrologic analysis
- Basin
- Fill
- Flow accumulation
- Flow direction
- Flow length
- Sink
- Snap pour point
- Snap pour
- Stream link
- Stream order
- Stream to feature
- Stream shape
- Watershed
**Reclassification**is replacing input cell values with new output cell values. The reasons to reclassify data are listed below:- To
**replace**values based on new information - To
**group**certain values together - To
**reclassify**values to a common scale - To
**set specific**cells to "NoData" or set "NoData" cells**to a value**