Creating a Shape File for the pour point

[Mark Blair]

Shannon,

I used the select tool and figured out the Object ID from the flow accumulation raster that I think is the best pour point. I know that I've forgotten something that we've learned or am having a very severe brain cramp, but when I try to "export data" from this selection process, I only get the option to export a .tiff rather than a shape file. The resulting .tiff does not list just the point (raster cell) that I selected. Using the .tiff, I can't use the snap pour point or watershed tools..........

Mark 

[Shannon Wing Belmont]

Yeah, Mark. you can't export raster data the same way you can export vector data.
The snap pour point tool creates a single cell output raster of the pour point for you, or you can create a shapefile (point) and digitizing a point in that single cell location.

Either a raster or vector file can be input to the watershed delineation tool for a pour point.

Hope that helps!

[Mark Blair]

Shannon,

Still must be having memory issues, but I reviewed previous labs, created a shape file (using ArcGIS help instructions) and tried to edit and add my point - didn't seem to work. I tried creating a file using the Snap Pour Point function but couldn't figure out what the input data was...

So, I took a wild guess and created a shape file the same way I created the Rupture Point in the last lab. Now I have a shape file with my pour point location data -- which I got from using the identify tool and getting the UTM grid from the location box.

For once, all of the other functions I used (raster to polygon, watershed delineation, etc) all worked on the first attempt. I ran the watershed tool with my designated pour point and then used the Snap Pour Point tool to "adjust" the pour point and compared the results -- same number of cells and no discernible difference in the outline of the watershed (guess I was pretty close in my estimation). I then compared these to the big_cotton file from the earlier lab -- there was a noticeable change in the NE corner where my watershed boundary was a bit truncated in comparison but there was a fairly consistent correlation around the rest of the perimeter. All in all, the big_cotton file had an area of 129.24 km2 and my watershed using the calculate geometry function after converting raster to polygon was 129.30, and using "raster math" (cell size x count) the area was 129.37 -- not too far off!

One interesting point that threw me for a while -- When I initially looked at my attribute tables for the watershed delineation, the count was displayed as 148621 cells. When I did the math, I was coming up up with 12.9 km2 -- off by a factor of ten... Out of curiosity, I took a look at the statistics tab and saw that the count was 1486219 - when I expanded the size of the table column for the count in the attribute table, lo and behold I could see the entire number was 1486219 rather than 148621 and the mystery was solved!

Thanks for the hints.

Mark

[Fidel Zebadua]

Hello Shannon,

Finally I could get the new shape (point) so now I tried to edit the shape files but the system sends a warning signal saying No editable layers so I did through the Editor button on the main menu. I click on start editing, it opens an new window and I click on big cottonwood because it is the only one that let me do some edits. But when I start making some edits nothing happens, only the big cottonwood boundaries illuminates. I stop editing and that is all. Then I try to snap pour point and the program runs good and nothing else. I cannot find the where the snap pour point results go. So without these results I cannot run the watershed tool. In the field Input raster or feature point data I have to place shape file point instead. The tool result sends a error. May I know what am I doing wrong? Thank you.

 

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[Shannon Wing Belmont]

Hi Fidel,

There are a couple of reasons you might not be able to edit the correct shapefile.

1. when you started editing, you didn't designate the correct folder containing your point shapefile. If you have layers in your map document that are contained in more than one folder, you will be given a choice to designate the folder you want to make available for editing. Make sure the point layer you want to edit is selected and has the pencil icon drawn across the icon that looks like a geodatabase container. 

2. If you do have the correct folder designated at the point layer you want to edit isn't appearing in the Create Features window, you need to "create a new template" to get that point layer added to the create features window. Review this video for a demonstration on creating new editing templates. It's from lab 5, on creating new templates.

Let me know if you don't get it worked out.

As far as not knowing where the output from the Snap Pour Point tool goes? There is a space to designate the output name and location. Are you saying your output is not found there? The output will just be a single cell, so it might not look like much.  You don't need to run the Snap Pour Point tool if you can just digitize the pour point location into a point shapefile. If you can get Steps 1 and/or 2 above to work, you can look at the flow accumulation layer either semitransparent over a hillshade so you can see the topography of the canyon. then digitize a point in the flow accumulation "channel" that is close to where you would define the entrance to the canyon. As long as the point is coincident with a cell in the flow accumulation channel, the snap pour point tool isn't necessary.