I am not a formally trained GIS professional nor is GIS a primary tool in my job. And therefore, without an incentive to optimize GIS workflows, I may not understand why one tool, although seeming to accomplish the same goal as another, may be better for a given task .

Sometimes answers or comments are given that imply or clearly state that the best tool to accomplish a given task is tool x and perhaps not the one suggested in the accepted/upvoted answer. Missing is a reason the other tool is not as good or the other better. I think this is important, to me anyway, to educate the asker and the answerer who has provided a not so good answer.

In this case, I would like to understand why Zonal Statistics is not the best tool for Count raster values in each polygon?

  • 1
    Zonal Statistics has limitations in how it calulates intersection and containment. This may offer some help gis.stackexchange.com/questions/261429/…. – Zipper1365 Dec 4 '17 at 17:18
  • Because Zonal Statistics creates statistics, the OP is seeking the count (statistic type VARIETY) of landuse within each polygon, so Zonal Statistics produces the intended result in one step. Using Tabulate Area the user has a table with the area of each land use for every input polygon and then must do some extra processing with multiple calculate field statements or write a python script to obtain the count of instances of landuse within each polygon. It is not unusual to have multiple tools that perform similar operations with only slight differences. – Michael Stimson Dec 4 '17 at 21:26
  • 1
    @Michael Stimson... Sounds like you are saying Zonal Statistics was the preferable tool as I suggested to the OP. The one step vs multiple steps explanation is helpful as well. – ZrSiO4 Dec 4 '17 at 21:41

Since I answered that question, I will explain why I said Tabulate Area is better than Zonal Statistics tool. The purpose of asker's question is to know the number of pixels of land use because he wants to calculate the area (I think) as he mentioned the pixel (30 x 30).

Therefore, I got the idea that he wants first to count the number of pixels then multiply the count with 900 (pixel area) so he can get the land use area within each polygon. In this case Tabulate area tool is the best because it gives directly the area in one step not two steps (count the pixels then multiply with pixel area).

Usually, it is more important to know the area of each land use class within each administrative area (polygon) than just the number of pixels. That is why Tabulate Area is very powerful because it makes it happen in one step.

Beside Zonal Statistics does not provide the option to count the pixels within each zone. It only provides these statistical options: Majority, Maximum, Mean, Median, Minimum, Minority, Range, Standard deviation, Sum, and Variety. There is no count pixels.

The Variety statistical option that you answered does not give the number of land use pixels within each zone (polygon), it says:

The number of unique values in each zone is assigned to all cells in that zone

| improve this answer | |
  • Thanks for explaining the logic for your answer. Given your interpretation of the OPs question, I agree Tabulate Area is the right approach... however in the statement ...I want to count the number of different land use values (they are in a 30x30m raster) in each of the small watersheds....the OP is clear about wanting different landuses in a watershed. Even though calculation of area may be an important and typical use of raster resolution, the OP did require area calculation. As for me I was only looking to understand the best use for each tool. This all helps. – ZrSiO4 Dec 5 '17 at 13:29
  • @ZrSiO4 I understand your point, if you look at my answer of the OP's question I mentioned that if you want the number of pixels of each land use, you need to divide the area by 900 which is another extra step to count the number of pixels. As Zonal Statistics doesn't have count option, Tabulate Area tool is still perfect for such purpose, but with extra step. – ahmadhanb Dec 5 '17 at 14:20

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.