What does 'Area' in Zonal Statistics refer to?

Question

Happy new year everyone!

Upon running a Zonal Statistics Table, one of the parameters shown is 'Area'. I assumed that this gives the area quantified in the amount of pixels. However, when I re-calculate the area from pixels to hectares, it does not give a logical number. Which makes me doubt whether 'Area' is in pixels or I may have done something wrong elsewhere. Does someone know more about this?

Willem_Bouw · Answer

David made me realize a significant error I made: I used Value Raster pixel size (cells of 500x500m) rather than the Zone Raster pixel size (cells of 30x30m=0.09ha). Still though, my outcomes are too large so there should be something else I do wrong. See the comment I made on David's reply

Willem_Bouw · Answer

The area of interest is the Bahia Negra basin in Paraguay. The country Paraguay itself is about 40.675.200 ha, with the Bahia Negra basin being a smaller area in the North of the country.

Upon conducting Zonal Statistics and summing all area type 'Area' values in Excel, I get 9.638.255.260 pixels for the entire area. Now an error I found thanks to you is that I used the pixels of the Value Raster (500x500=25ha cells) rather than the Zone Raster (30x30=0.09ha cells). So thank you for making me realize my mistake 🙂 However, changing this, it would give the total area the size of 9.638.255.260pixels * 0.09ha = 867.442.973 ha, which is still too much. So there must be something else I do wrong.

Added are some screenshots of the Area values given in the Zonal Statistics table (value stands for land cover), and the land cover of the regarding map of the area of Bahia Negra

Land cover value 3 (green) and 15 (yellow) should be the only ones with a significant amount of Area. The other land cover values are barely represented in the map so it is odd that they are given this big amount of pixels in the Zonal Statistics Table

EDIT: I just realize that the column 'Count' gives the amount of pixels. So in that case, 'Count' should be considered as the area given in pixels, rather than the 'Area' column. That would also give more logical values. But what does the column 'Area' refer to then?

DavidPike · Answer

Your math seems fine.  Might be a good initial check if you sum the Area values in the table that should give the count of all Zone pixels in your extent. that sum value * 25 should give the total extent area (in Hectares) If you don't have any NoData etc.  How far off are your calculations?  Also easy to confuse the value raster with the zone raster.

Would you be able to share any screenshots etc. ?