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#1
yeneneshabebe

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Hi all ,

Thankyou very much. I have succeded to do the slope map. Now ,I am trying to show Irrigated areas per different districts. The irrigated area value for each district is in hectars and each district has exact irrigated land value. I am trying to use proportional symbols. Am I correct?

Is 5 the maximum number of symbols? The maximum value which is represented by the symbols is 10,000Ha. But I have values more than 30000 or 50000Has in some distriocts. What mistake I have done ? or is better to use another option.




Thanks,


Yenenesh

#2
Hans van der Maarel

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Thankyou very much. I have succeded to do the slope map. Now ,I am trying to show Irrigated areas per different districts. The irrigated area value for each district is in hectars and each district has exact irrigated land value. I am trying to use proportional symbols. Am I correct?

Is 5 the maximum number of symbols? The maximum value which is represented by the symbols is 10,000Ha. But I have values more than 30000 or 50000Has in some distriocts. What mistake I have done ? or is better to use another option.


You could use proportional point symbols for this. I.e. the area of the symbol is linked to the value for the irrigated area.

It's not clear whether the software you're using is trying to limit this to 5 distinct classes (which would be bad), or just showing a legend with 5 classes (which would be good, though the range shown in the legend would have to cover more of the actual data range to be useful). Could you elaborate on this? Maybe post a screenshot?
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#3
SaultDon

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The maximum value which is represented by the symbols is 10,000Ha. But I have values more than 30000 or 50000Has in some distriocts. What mistake I have done ?


In ArcGIS, you may be experiencing a "sampling" issue. By default sampling is set to 10000 records (the first 10000 records in the attribute table). Not sure why, but I think its to prevent unwittingly crashing/freezing the system say when you try to symbolize millions of features, for instance....

Once you click on one of the "graduated" symbology options. you may get this warning:

Attached File  maxsample_err.png   62.42KB   23 downloads


Open up that features attribute table to get the TOTAL features and write that down somewhere or remember it.

Go back to the "graduated something" option in your symbology tab and click the Classify... button then click Sampling...

Increase the Maximum Sample Size to something larger than the total amount of features, example:
My features have a total of 22478 records. So my sampling is set to 25000.

Attached File  sampling_increase.png   83.08KB   18 downloads


Now the Count should include all possible values and give you the full range you are looking for.
You can also change the amount of Classes using the pulldown menu to something greater than 5:

Attached File  count.png   59.14KB   17 downloads


You can only adjust sampling in the 'graduated' type symbologies, not proportional symbols for instance.

What symbology option you use is entirely dependent on your data: Data Evaluation and Classification is an article I read over sometimes to help me choose an 'appropriate' method for displaying information on maps.

#4
yeneneshabebe

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Hi,

The ArcGIS is not limiting the number of classes .It gives options up to 12 classes. After setting the class number different than 5 the class which will be displayed willbe 5 again. This is the screen shoot of the Arc map window. If the size of the symbols is affected by the irrigated area,is it important use some normalization field ? How can I decide the smallest and the largest point symbol?


It says I don't ahve permission to upload a file. So I couldn't display the screen shot.

Thanks very much for all ur support.

Yenenesh

#5
Hans van der Maarel

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It says I don't ahve permission to upload a file. So I couldn't display the screen shot.


Could you try again? I've validated your membership (for some reason you were still set to "New Member", despite being a regular contributor, sorry about that) so it should work now.
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#6
yeneneshabebe

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It says I don't ahve permission to upload a file. So I couldn't display the screen shot.


Could you try again? I've validated your membership (for some reason you were still set to "New Member", despite being a regular contributor, sorry about that) so it should work now.


Hello Hans,

It still says I don't have the permission. Now the number of classes can be changed but I don't know how it is solved. My user account was corrupted i don't know it may because of that. But still it can't accomodate values more than 10000,when the number of calsses increased the classification goes down to small values not to the other way.


If the size of the symbols is affected by the irrigated area,is it important use some normalization field ? How can I decide the smallest and the largest symbol size?



Thanks very much for all ur support.

Yenenesh




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