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#1
GISMan83

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Hello,

The Project: Modeling a slope development district for the city (Going from a hand-tool method to a GIS method).

Originally the Slope Development District was developed using only hand tools, however, the city wants to find a way to do it using ArcGIS 9.2

The parameters as listed by city ordinance:

The Slope Development District boundary has been established at an elevation contour immediately above or below which a twenty-five foot vertical span of mountainside has a slope of fifteen percent or greater and the district is to include those contiguous parts of mountains or hills that exhibit at least one hundred feet of relief as measured from the lowest elevation contour that bounds the fifteen percent or greater slope to the highest contour of the district as defined herein.

In addition, the upper boundary shall be extended fifty feet (horizontal distance) beyond the elevation contour immediately below which a twenty-five foot vertical span exhibits a slope of fifteen percent or greater.

The data:
DEMs of the city
Shapefile of the city boundaries
Elevation Contours (50ft, 10ft, and 2ft intervals)
TINs of the city

The problem:
The twenty-five foot vertical span of mountainside. How could I measure this or create a layer or feature class for this? I am open to any suggestions or advice that anyone else could give.

#2
Hans van der Maarel

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So...

Basically you want to find areas where over a vertical distance of 25 meters the slope is at least 15%?

I think I might be able to pull that off, but not with Arc (that is to say, I don't use Arc, it may very well be possible in it too). But it'll be difficult and I'm wondering whether the manual method isn't still the quickest
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#3
GISMan83

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So...

Basically you want to find areas where over a vertical distance of 25 meters the slope is at least 15%?

I think I might be able to pull that off, but not with Arc (that is to say, I don't use Arc, it may very well be possible in it too). But it'll be difficult and I'm wondering whether the manual method isn't still the quickest


Yes, that is exactly what I am trying to do. I also tend to agree with you that doing it by hand is going to be the quickest method. The city planner wants it done using GIS though.

I've actually ran a model that found areas with a slope of at least 15% and it actually fit the results of the manual method by about 80%. I'm currently working on cleaning that data up.

However, if there is a way, that I can figure out how to find areas where there is a vertical distance of 25 meters and a slope of at least 15% that would be best since it would fit the parameters for the slope development district outlined by the city's ordinance. So I'll keep trying to figure it out. Thanks for the input.

#4
Hans van der Maarel

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However, if there is a way, that I can figure out how to find areas where there is a vertical distance of 25 meters and a slope of at least 15% that would be best since it would fit the parameters for the slope development district outlined by the city's ordinance. So I'll keep trying to figure it out. Thanks for the input.


You could dissolve those results, then overlay them with the contours and see what the difference between the highest and lowest overlapping contour is.
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#5
GISMan83

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You could dissolve those results, then overlay them with the contours and see what the difference between the highest and lowest overlapping contour is.


Thanks for the idea Hans. I will try that next.

#6
James Hines

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I seem to remember doing a major forestry atlas project back in 2002 using the entire suite of ArcGIS 8.1. Slope mapping was included as part of the project so bare with me on the steps I took to create this plate:

ArcMap
--------
- A DEM was created from contours
- from the DEM I had convert it convert to raster using 3D Anaylst
- the next step was to use Spatial Anaylst to create a slope map of the location ( look under the Surface Analysis option)
- after opening the symbology through the properties then hit the classification tab then hit the % option & type in the required % values eg 0-3%....15-25% etc.

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#7
GISMan83

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I seem to remember doing a major forestry atlas project back in 2002 using the entire suite of ArcGIS 8.1. Slope mapping was included as part of the project so bare with me on the steps I took to create this plate:

ArcMap
--------
- A DEM was created from contours
- from the DEM I had convert it convert to raster using 3D Anaylst
- the next step was to use Spatial Anaylst to create a slope map of the location ( look under the Surface Analysis option)
- after opening the symbology through the properties then hit the classification tab then hit the % option & type in the required % values eg 0-3%....15-25% etc.


Thank you Hasdrubal for your input. Through the advice given by both you and Hans I have calculated the percent slope for the area in question.

Now I have to figure out a way to measure the undefined 25ft vertical span of mountainside and to combine that with the percent slope in order to define the Slope Development District.




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