Differences

This shows you the differences between two versions of the page.

Link to this comparison view

Both sides previous revision Previous revision
Next revision 		Previous revision
calc_areas [2011/04/20 22:56]
hermann [Output] 		calc_areas [2026/08/28 03:09] (current)
hermann Sync from local documentation review
Line 1: Line 1:
-====== Calc Areas ====== ​+====== Calc Areas ======
  
 ===== Description ===== ===== Description =====
Line 7: Line 7:
 ===== Inputs ===== ===== Inputs =====
  
-^ 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 ​                                ​^ +^ Name  ^ Type  ^ Description ​ ^ Default Value  ​^ 
-| Areas In Cells         | [[Lookup Table Type|Lookup Table  ​]] | Area of each map category ​in cells. ​        ​| +| 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  ​| 
-| 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. |+===== Outputs ===== 
 + 
 +^ Name  ^ Type  ​^ Description ​ ^ 
 +| Areas  | [[Table Type]] ​ | Area of each source feature, ​in cells, hectares, and square meters. ​ |
  
 ===== Group ===== ===== Group =====
  
-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. 
 + 
 +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]]