9A flow accumulation issue

[Bryan Christensen]

Hi everyone.  I'm stuck.

I ran the flow accumulation tool and got an output raster.  It added to my layers and looks like the picture in the lab.  But when I go to the raster's symbology to change its color ramp into 2 classes, I don't have the option.  The symbology tab "shows" this in a 'stretched' format.  When I click on 'classified' like the lab picture shows, I get an error that "this dataset does not have valid histogram required for classification method, run calculate statistics tool to generate histogram."  

did anyone else run into this snag?

[Shannon Wing Belmont]

Hi Bryan. You should be able to say yes to calculate statistics to generate the histogram. Does that work?  the message is just telling you that Arc needs to determine the full set of values for the raster so it can figure out what the histogram looks like and can then determine where the natural breaks are and all the other things for classifying the data.

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Shannon Belmont

Quinney College of Natural Resources
Utah State University
5210 Old Main Hill
Logan, UT 84322-5210

[Bryan Christensen]

i just calculated stats in the data management tool.  we'll see what happens. 

Bryan Christensen

Dedicated Hunter/Volunteer Services 

Program Coordinator

Phone 801-200-4400

[Bryan Christensen]

I have an ok button,  but haven't found a way to run the calculate statistics yet.  Here's a screenshot of what I'm seeing.  

Sent from my iPhone

[Shannon Wing Belmont]

Bryan, Did you run the "calculate statistics" tool on the raster? Give that a try.

You can either run the tool, or in ArcCatalog, navigate to the raster, right click on it and choose to calculate statistics.

[Bryan Christensen]

i ran the calculate statistics tool, and that seemed to work.  maybe??

I went back into the raster layer and was able to get into the classification-- changed it to 2 classes-- changed the jenks to manual-- and changed my symbol coloring and classified it again.

my range is not 0-16503 and 16503-1490093.  I have 0-5847901 and 5847901-17543703.  much bigger, but i'm guessing that is because i haven't clipped the watershed yet.

the problem now is my accumulation flow layer doesn't show up anywhere.  I've checked all my transparancies, zooming to layers, etc.  

 

On Mon, Apr 8, 2013 at 10:16 AM, Shannon Wing Belmont <swb....@gmail.com> wrote:

Bryan, Did you run the "calculate statistics" tool on the raster? Give that a try.

You can either run the tool, or in ArcCatalog, navigate to the raster, right click on it and choose to calculate statistics.

[Shannon Wing Belmont]

Bryan~ Good progess.

Other tricks: turn the visibility on and off, make sure the drawing order is correct, Click the "refresh button (the two circling arrows on the bottom left of your data window next to the data view/layout view buttons.

OR just start a new map document, and just add the flow accumulation layer.

(and anything else you find you need as you go.) No need to work in big clunky map projects if you are being careful with your data management :)

[Bryan Christensen]

grrr.  I've tried all the tricks I can think of with this one.  I'll just back up a few steps and re create the accumulation raster again.  My flow direction raster went fine.  So I must have done something wrong between those steps.

I also got word from the IT department today that my new (functioning) laptop has arrived and they'll be taking my current one (a horrible disaster of a computer) away soon. Hopefully it will only be a day long issue.  

[nikol...@hotmail.com]

So I have been having an problem with the flow accumulation.  It is only showing 1 main flow system.  I don't have any other flows, just the one down the middle, the main river.  I don't have any in the main watershed that I will be clipping later on.  What did I do wrong?  I have done the flow accumulation a few times?  Did I mess up with the flow direction raster? Can I get some help please?

Thanks!  Nikol :)

[Shannon Wing Belmont]

Hi Nikol,

Probably nothing done wrong, might just be a symbology issue. Work on reclassifying the flow accumulation surface to 2 classes to display more of the "network."

On Wed, Apr 10, 2013 at 10:10 AM, nikol...@hotmail.com <nikol...@hotmail.com> wrote:

So I have been having an problem with the flow accumulation.  It is only showing 1 main flow system.  I don't have any other flows, just the one down the middle, the main river.  I don't have any in the main watershed that I will be clipping later on.  What did I do wrong?  I have done the flow accumulation a few times?  Did I mess up with the flow direction raster? Can I get some help please?

Thanks!  Nikol :)

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[Bryan Christensen]

I just re ran mine and got the same result.  Looks like it's the Jordan River/canal.  

On Wed, Apr 10, 2013 at 10:10 AM, nikol...@hotmail.com <nikol...@hotmail.com> wrote:

So I have been having an problem with the flow accumulation.  It is only showing 1 main flow system.  I don't have any other flows, just the one down the middle, the main river.  I don't have any in the main watershed that I will be clipping later on.  What did I do wrong?  I have done the flow accumulation a few times?  Did I mess up with the flow direction raster? Can I get some help please?

Thanks!  Nikol :)

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[Shannon Wing Belmont]

Bryan,

Can you send me a screen shot of your flow accumulation raster with the range of values in the attribute table?

Try clipping (Data Management clip) the flow accumulation raster to the watershed boundary then displaying the values in 2 classes (0-5000 and 5000 to the max value).

The range of values you reported for flow accumulation above (0-5847901 and 5847901-17543703) looks totally reasonable for the unclipped FA raster.

In a new map doc, I'm not sure why you can't get it to load or display properly?

[nikol...@hotmail.com]

This is what my computer is showing.  I ran the calculate stats tool and I am not able to open my attribute table. All I get is the 'channel'.  Where do I go from here?

Thanks! Nikol :)

[Bryan Christensen]

There is a video tutorial that is really helpful for this part in Lab 9a.  it is called stream order.  somehow i missed that one until now.  

you basically go back to the symbology page that you were on.  switch to Manual, and then you can actually chose the value in the window to the left of the graph.  

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[nikol...@hotmail.com]

Thank you so much Bryan!!  That is exactly what I needed to do!  

Nikol :) 

[Bryan Christensen]

indirectly, the thanks is to Shannon, she got me that far in another thread.

good luck.  

On Wed, Apr 10, 2013 at 3:20 PM, nikol...@hotmail.com <nikol...@hotmail.com> wrote:

Thank you so much Bryan!!  That is exactly what I needed to do!  

Nikol :) 

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[Fidel Zebadua]

Hello Shannon,

I am in lab 9a too. Finally I got my stream order with 4 different "streams" (4 different colors). Then I used the "Raster to polyline tool"

for convert the raster to vector data set. It worked good but I only get one single "legend", I mean the whole new vector dataset is in one single color,

everything is plain green. This way I can measure the length of the main stream by selecting by rectangle, and clicking shift to adding at the current

selection, open the attribute table and summarize by hand each segment length. What I want is to classify the different kinds of streams and 

give them a different colors and classify them into the legend, and finally to get the length of each stream class. How can I do this please? Thank you.  

[Fidel Zebadua]

I got it!

After get my raster into a vector dataset, I right click on it and opened the properties option. I went to symbology tab and set it in the left corner

 to quantity. This way I was able to change the values to cells on grid (something like that),and the number of classes. I changed to 3 classes

(I placed together 3 and 4) and change the line color and width. For obtaining the length of each stream class I selected by hand using the

selecting by rectangle and shift button, then open the attribute table and see the selected items only. I right click on the head column

"Shape_lenght", then click on statistic and a little window will be opened. This window shows some numerical information. Within this information

is the length of the selected items. I hope I could help someone with this information. See you and I think it is time to go to bed :)