Reclass by ranges of values
You may want to reclassify a range of values to an alternative value and another range to a different alternative value. For example, on the input land-use raster of a building suitability model for a house, all the residential and human activities values range from 0 to 9, the forest values range from 10 to 19, and the agriculture values range from 20 to 29. You may want to assign a suitability of 1 to the land-use values 0 through 9 (the human activity), 5 to land-use values between 20 and 30 (the agriculture), and 10 to land-use values between 10 and 19 (the forest). It would be tedious if you had to explicitly specify each existing land-use value and the alternative values, since there are many values.
The capability to reclassify ranges of values becomes more critical when reclassifying continuous data. For example, if you were reclassifying elevation values for a bird habitat model, you might reclassify elevation values of 1,000 to 1,500 meters above sea level to 10; 750 to 1,000 to 8; and so forth. Since elevation is a continuous surface, cell values may include values such as 1,005.34, 1324.50, 743.89, and 312.45. It would be difficult and time consuming to specify each individual elevation value on the input raster and its corresponding alternative value. Also, chances are you wouldn't need to, because most analyses would be applied to elevation values grouped into ranges.
When reclassifying by ranges of values, the reclassification tools require the lower and upper bounds of the existing values on the input raster and the alternative value to assign to the range of values. All values on the original raster that fall within the specified range of values will receive the alternative value assigned to that range. The range boundary breaks are handled differently in the various tools. That is, if two ranges are specified, such as 1 to 5 equal to 100 and 5 to 10 equal to 200, the value 5 will usually be assigned to the value 100 and 5.01 will be assigned to 200 as output values.
The following example reclassifies the original values from base raster by ranges to new reclassified values:
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Example of reclassification by value ranges |
Reclassifying ranges of values is usually done when the input values are continuous—for example, elevation or distance—or when changing groups of categorical data as in the land use example above.
Ranges of values can easily be reclassified through the Reclassify tool. The tool dialog box also allows manual, equal interval, defined interval, quantile, natural breaks (Jenks), and standard deviation classification methods for the classification of the original data.