Raster Data Analysis Environment: Cells and Masks (Especially for GATE-Geospatial 2022)

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Raster data analysis is based on cells and raster. It can be performed at the level of individual cells, or groups of cells, or cells within an entire raster. Some raster data operations use a single raster; others use two or more rasters. Raster data analysis also depends on the type of cell value (numeric or categorical values) .

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The analysis environment refers to the area for analysis and the output cell size. The area extent for analysis may correspond to a specific raster, or an area defined by its minimum and maximum x-, y-coordinates, or a combination of rasters.

Combining Rasters

Given a combination of rasters with different area extents, the area extent for analysis can be based on the union or intersect of the rasters. The union option uses an area extent that encompasses all input rasters, whereas the intersect option uses an area extent that is common to all input rasters.

This Image Shows Data Analysis Environment in Raster Data an …

Mask

A mask identifies those cells within the analysis extent that will be considered when performing an operation or a function. Setting an analysis mask means that processing will only occur on selected cells and that all other cells will be assigned values of NoData.

Illustration 2 for Combining_Rasters

Analysis Mask

An analysis mask can also determine the area extent for analysis. An analysis mask limits analysis to cells that do not carry the cell value of “no data.” No data differs from zero. Zero is a valid cell value, whereas no data means the absence of data. For example, one option to limit the analysis of soil erosion to only private lands is to code public lands with no data. An analysis mask can be based on a feature layer or a raster.

Cell Size

You can specify the output cell size or resolution, or you can take the default. The default cell size, or resolution, for analysis results is set to the largest cell size of all the input raster datasets for the tool.

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The default output resolution, when a feature class is used as input, is the width or height of the extent of the feature class divided by 250.

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