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calc_areas [2011/11/20 18:20] admin |
calc_areas [2026/08/28 03:09] (current) hermann Sync from local documentation review |
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| - | ====== Calc Areas ====== | + | ====== Calc Areas ====== |
| ===== Description ===== | ===== Description ===== | ||
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| ^ Name ^ Type ^ Description ^ | ^ Name ^ Type ^ Description ^ | ||
| - | | Categorical Map | [[Categorical Map Type|Categorical Map]] | Map containing classes or categories. | | + | | Source | [[Categorical Map Type]] | Map whose non-null cells correspond to categories or classes. | |
| - | ===== Output ===== | + | ===== Optional Inputs ===== |
| + | |||
| + | ^ Name ^ Type ^ Description ^ Default Value ^ | ||
| + | | Use Authalic Area | [[Boolean Value Type]] | If true, the area of each cell in a geographic (Lat/Long) grid is computed using an authalic sphere, which preserves surface area during projection. This improves the accuracy of area calculations across all latitudes by avoiding distortions. If the grid is geographic but this option is false, all cells are treated as having the same area, calculated by treating the length of one degree of latitude or longitude as a constant 111255 meters. This is an advanced port. | Yes | | ||
| + | |||
| + | ===== Outputs ===== | ||
| ^ Name ^ Type ^ Description ^ | ^ Name ^ Type ^ Description ^ | ||
| - | | Areas In Cells | [[Lookup Table Type|Lookup Table]] | Area of each map category in cells. | | + | | Areas | [[Table Type]] | Area of each source feature, in cells, hectares, and square meters. | |
| - | | Areas In Hectares | [[Lookup Table Type|Lookup Table]] | Area of each map category in hectares. | | + | |
| - | | Areas In Square Meters | [[Lookup Table Type|Lookup Table]] | Area of each map category in square meters. | | + | |
| ===== Group ===== | ===== Group ===== | ||
| - | [[Functor List#Map Algebra|Map Algebra]] | + | [[Functor List#Map Algebra | Map Algebra]] |
| ===== Notes ===== | ===== Notes ===== | ||
| - | Only the areas corresponding to class or categories defined in the input map header are calculated. | + | Only the areas of classes or categories present in Source's categorization are calculated; other values are ignored. |
| - | If the cell dimensions are represented using degrees, the areas in hectares and square meters becomes an approximation. All cells are always supposed to be of the same size. | + | The resulting table has the following format. |
| + | |||
| + | ^ Column Name ^ Key or Data? ^ Column Type ^ Description ^ | ||
| + | | "Category" | Key | Real | Category in the feature map | | ||
| + | | "Area_In_Cells" | Data | Real | Area of corresponding category in cells | | ||
| + | | "Area_In_Hectares" | Data | Real | Area of corresponding category in hectares | | ||
| + | | "Area_In_Square_Meters" | Data | Real | Area of corresponding category in square meters | | ||
| + | |||
| + | **References** | ||
| + | |||
| + | Santini, M., Taramelli, A. and Sorichetta, A., 2010: [[https://www.researchgate.net/publication/220606016_ASPHAA_A_GIS-Based_algorithm_to_calculate_cell_area_on_a_latitude-longitude_Geographic_regular_grid|ASPHAA: A GIS-Based Algorithm to Calculate Cell Area on a Latitude-Longitude (Geographic) Regular Grid]]. Transactions in GIS, 14(3), 351-377. | ||
| ===== Internal Name ===== | ===== Internal Name ===== | ||
| CalcAreas | CalcAreas | ||
| + | |||
| + | ===== Usage examples ===== | ||
| + | |||
| + | See practical examples of this functor in [[lesson_9|Lesson 9: Working with maps and tables]] | ||