Defining Buffers, Setbacks and Spreadable Acreage

From Wikiagro.com

This exercise is included in the tutorial: GeoAgro for CNMP Development

Each State has specific setbacks requirements, available at http://www.cares.missouri.edu/snmp/setbacks/index.html . Setbacks may include property lines, ponds, streams, well, etc. In this session, you will be able to:

• Define setbacks and buffers for a well, stream and property line.
• Calculate spreadable acreage for each field, by substracting the buffer/setback area.
  
  

 

Contents 1 Exercises 1.1 Exercise 01 - Download sample data 1.2 Exercise 02 - Plan your buffers and setbacks 1.3 Exercise 03 - Create setback from property boundary 1.4 Exercise 04 - Create buffers from stream and well 1.5 Exercise 05 - Define the spreadable acreage area 1.5.1 Copy 1.5.2 Substract 1.5.3 Copy to destination layer 1.5.4 Spreadable acreage area

Exercises

Exercise 01 - Download sample data

Start GeoAgro GIS by double clicking on its icon at your desktop; you may also run it by using the Windows® Start menu.

The Project Selection window will pop up.

Follow the steps from this link to download the sample datset for this tutorial and create the project 'Sample CNMP' as indicated there.

Exercise 02 - Plan your buffers and setbacks

1. Zoom in to the farm by double clicking on the “Fields_NRCS” layer in the left panel. You may use the Zoom Tools to zoom in or out.
   
   
2. Since this farm is in Iowa, we need to apply the following buffers and setbacks according to http://nmplanner.missouri.edu/software/setbacks.asp.
   
   

Feature	Type	Distance
Property boundary - irrigated liquid manure	line	100 ft
Drinking water well - not incorporated applications and irrigated manure (vegetative buffer)	point	50 ft
Water source- not incorporated applications and irrigated manure (vegetative buffer)	line	50 ft

Thus, in our farm we will create a 100ft setback from the property line and a 50ft buffer from the well and stream.

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Exercise 03 - Create setback from property boundary

What we are going to do first is create a 100ft offset from the property line. Follow the instructions below:

1. Make the “Tracts” layer active by selecting it.
   
   
2. Choose the Point selection tool in the Navigation panel.
   
   
3. Click anywhere inside the “Tracts” polygon to select it.
   
   
   
4. In the Edit Layer's Objects Panel there is a tool called Offset . Click on it.
   
   
   
5. The “Offset” window will come up. Since we want to create another polygon in order to set our setback, we need to click on the “Polygon to Polygon” tab. The option “Don’t modify” must be selected
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6. We want to create a 100ft setback from the property line; this is a new polygon smaller than the tract polygon. Therefore, the offset must be negative: -100. Of course, “Feet” is the unit of measurement. Finally we need to select the target layer. In this case, the “Buffers & Setbacks” layer is the one we are going to use. The picture below shows the right configuration.
   
   
   
7. See the resulting polygon.
   
   
   

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Exercise 04 - Create buffers from stream and well

Now, we are going to create buffers around the Stream and well. Since the explanation is unique for both, we will only focus on the stream buffer.

1. Make the “Streams” layer active by selecting it.
   
   
2. Choose the “Rectangle selection tool” from availableSelection tools
   
   
3. Draw a rectangle including any part of the stream to select it.
   
   
   
4. In the “Objects Panel” there is a tool called “Buffer”. Click on it.
   
   
   
   
   
5. We will define a 50ft offset, “Feet” is the unit of measurement and the “Buffers & Setbacks” layer is the target. See the picture below.
   
   
   
6. Repeat the procedure for the 50ft buffer from well. Both, the buffers and setback are shown in the following picture.
   
   
   

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Exercise 05 - Define the spreadable acreage area

Now we are going to define the spreadable acreage area, by substracting the polygons created from the buffer operations. For this, we will use the “Delete Overlaps” tool.
As you can see, there is a portion of the property line setback which is drawn over the farmstead. We also need to substract it.

Copy

Since we are going to substract all the polygons in the same step, we need first to copy the homestead and the upper left corner Fields into the “Buffers & Setbacks” layer.

1. Make the “Fields_NRCS” layer active by selecting it. 
    
   
2. Choose the Point selection tool from the Selection Tools in the “Navigation panel”. By simultaneously pressing the 'CTRL' key, you can select or unselect more than one field.
   
   
3. Select the homestead and the upper left corner Fields.
    
   
   
4. In the Edit Objects Panel  click on the tool Copy Object .
   
   
   
   
   
5. Finally, select “Buffers & Setbacks” as target layer and click on copy.
   
   
   

Substract

Once the copy is completed, we can substract the buffers and homestead/upper left fields from the original property setback area, to define the spreadable acreage area:

1. Make the Buffers & Setbacks layer active by selecting it.
   
   
   
2. Click on the Point selection tool and then on the large polygon.
   
   
3. Click on the Edit Objects Panel → and then click on Delete Overlaps tool .
   We have substracted the stream and well buffer areas and the farmstead/upper left fields from the large polygon, as shown below:
   
   
4. Now repeat the process to define the spreadable acreage for the upper left field - create setback from property boundary, create stream buffer, copy the largest field to the buffer & setbacks layer, and use the delete overlaps tool.
   Your screen should now show both spreadable acreage areas, as below:
   
   
   

Copy to destination layer

As final step, you may copy the spreadable acreage areas to the corresponding layer.

1. Make sure the Buffers & Setbacks is active by clicking on it.
   
   
   
2. Select the two spreadable acreage areas, go to the Edit Objects panel → then click on Copy object and choose “Spreadable Acreage” as target layer.
   
   
3. The two spreadable acreage areas are copied to the corresponding layer, as shown below:
   

 

Spreadable acreage area

Let’s see what the spreadable acreage area for our farm is.

1. Make sure that the Layer 'Spreadable Acreage' is active by clicking on it
   
   
   
2. Select the two spreadable acreage areas, using available Selection tools.
   
   
3. Click on the Info tool in the Navigation toolbar and the spreadable acreage for both fields will be shown, it's 120.30 acres for the larger field, and 2.13 acres for the upper left field.