What is the "Count" field in the attribute table of the Combine Tool

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06-22-2019 02:42 PM
BaileyFredlund1
New Contributor III

Hello everyone. I am wondering what exactly the count field is after running the combine tool. I checked out the ArcGIS and ArcPro website helps for this tool but it didn't give me a straight answer. I should probably know this answer... I think it is the count of pixels for each combination created. I want to get a confirmation though so any information will help! Thanks in advance. 

Not related to this question but.... I used this tool for a post-classification change analysis. If there is a better way to do this please let me know.

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DanPatterson_Retired
MVP Emeritus

It counts pixels and here is why

Take the result from your combine. 

Assume you had a 10m cell size.

Use Copy Raster  to copy the raster, but in the Environments section, set the cell size to 5 m (or half of what you have)

The output raster (assuming it is done correctly) will have a cell count 4X the original since you halved the cell size.

The only time cell count will equal area is when you have a 1x1 unit cell size

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DanPatterson_Retired
MVP Emeritus

Combine—Help | ArcGIS Desktop 

it is the count of the combinations... technically, since each cell has an area, it also represents the spatial area (ie square meters) and the location where that combination is found

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BaileyFredlund1
New Contributor III

Okay, I see. So it isnt the pixels? It is already converted to spatial area? Thanks for response!

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DanPatterson_Retired
MVP Emeritus

a pixel represents an "area"... aka  a square location

now  each "area" (aka, pixel) has an 'area' (ie square meters).

so the pixel count represents the "areas" that have those combinations, … say 10 pixels.  if each pixel has an area of 3m x 3m, then the 'area' is 90 meters squared.

clear as mud, but rasters are represented by square pixels (usually), each pixel has an area and the total area of an attribute or combination of attributes if 'combined' represents the places where the combination occurs and the 'area' with planar units.

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BaileyFredlund1
New Contributor III

Hello Dan thanks for reply. I understand the relationship between pixels and areas. Just wondering which one Count is providing. I understand I can do simple calculation if the count is pixels, and do a similar but opposite calculation if the count is square meters. Thanks for your help.

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DanPatterson_Retired
MVP Emeritus

count the pixels multiply by the area of 1 pixel = total area

the count is definitely not square meters. 

Count is measured on an interval scale (no decimals possible( and area are ratio data (decimals possible)

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BaileyFredlund1
New Contributor III

My question is just is the Count field in pixels or a distance measurement. I know how the two relate. That explanation is not needed. 

Is Count pixels or area measurement? That is all. 

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DanPatterson_Retired
MVP Emeritus

It counts pixels and here is why

Take the result from your combine. 

Assume you had a 10m cell size.

Use Copy Raster  to copy the raster, but in the Environments section, set the cell size to 5 m (or half of what you have)

The output raster (assuming it is done correctly) will have a cell count 4X the original since you halved the cell size.

The only time cell count will equal area is when you have a 1x1 unit cell size

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BaileyFredlund1
New Contributor III

Thanks for your time! This made it clear.

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