FOR557 – 04
Exercise 5_04
Heads Up Digitizing
Due: 11/5
Overview
This is an exercise in heads up digitizing and is based on what you learned in Module 5. I don’t
give a lot of instruction re the editing so you have to figure it out from the Module and help. The
situation is that you have been asked to determine the area of agricultural fields in the area
shown in Figure 1. This is because the mass marketer wants to build a store in the area and the
planning board wants to know how much agricultural land will be lost from the immediate area
(this is a little unreal but I don’t think you want to digitize all the ag lands in the 4 images – but
you are free to do so if you want to. The area the store wants is specified by GPS points and its
approximate position is shown in figure 1.
What gets turned in
A map based on a map image similar to that in Figure 1 showing the agriculture areas, the roads
in the area classed route and ownership (you will have to find a map of Lewis county), the river,
and the area that the store wants. Add a page of answers to questions in whatever format you
think appropriate. This must include a discussion of the areas of the fields and the area of the
store lot along with owner’s names. End with a reflection page.
The Assignment
1.
2.
3.
4.
5.
Download the MrSid orthos from the schedule page (4 of them)
Load them into ArcMap.
What are the Coordinate Systems of the images? Make note of it.
Add the some roads data (Lewis County). What source did you use?
Now digitize the data.
5.1. In ArcCatalog make 5 new shape files – 2 polyline shapes (roads, river), 2 polygon
shapes (aglands, store), and a point shape (houses). The procedure for one of these is
outlined below.
5.1.1. Right click on your workspace folder in ArcCatalog and select New and then
Shapefile.
o The Create New Shapefile dialog opens. Should look somewhat familiar.
o Select feature type of point, line, or polygon as required
o Description is unknown so you have to edit the new file so that its coordinate
system and extent match that of the image.
• Click Edit and then click the Import button
• Select one of the image files and click Add
5.2. Now that you have the 5 empty shapefiles you can add them to ArcMap. You should
know how to do that by now.
5.3. Digitize the agricultural polys shown in Figure 1 (last page). Mine are NOT exact so
don’t try to duplicate that exactly. But do make abutting feature edges the same.
(Topology?)
5.4. You need to add the area of the polys to the attribute table since it was not calculated.
Here is how (and the procedure is in Help also. Search for Tables, then within that,
Area, and within that, Calculate).
5.4.1. Open the Table for the poly layer
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FOR557 – 04
Exercise 5_04
Heads Up Digitizing
Due: 11/5
5.4.2. The box on the below contains the procedure (from Help with slight modifications
by me). You will be entering 4 lines of Visual Basic for Apps (VBA) code and you
must get it exactly right – computers are fast but stupid and don’t know what you
mean only exactly what you say! It took me several tries to get it right! The major
reason was the I in IArea looks like a lower case L (l) in the code font and l does
NOT work!
5.4.3. This should calculate the area of your polys in map units (which are?)
Updating Polygon areas for a shapefile
1.
Open the attribute table for the layer of interest and create a field called Area (or fiddlesticks, the name does
not matter). Add a new field for area or whatever by clicking the Options button (lower right) and selecting
Add Field. (To add a new field, you cannot be in an editing session. )
2. What does matter is that you make the Type double, precision like 15 and scale like 3. 15 is the total width
of the number including the point. The example above results in numbers like ppppppppppp.sss or 1234512345.123. Has to be able to hold your calculated values!
3. NOTE: You can make calculations without being in an editing session; however, in that case, there is no
way to undo the results -- but you can recalculate field values..
4. Right-click the shapefile layer you want to compute areas for and Open its Attribute Table.
5. Right-click the new field heading and select Calculate Values.
6. Check the Advanced check box. Å easy step to miss! It’s a check box between the two Text windows.
7. Type the following VBA statement in the first text box: (See example on last page). You can copy and paste
the code also.
Dim dblArea as double
Dim pArea as IArea
Set pArea = [shape]
dblArea = pArea.area
8. Type the variable dblArea in the text box directly under the area field name.
9. Check the code carefully – the computer will do exactly what you tell it to, right or wrong.
10. Click OK.
Updating Perimeter is the same except the code is
Dim dblPerimiter as double
Dim pCurve as ICurve
Set pCurve = [shape]
dblPerimiter = pCurve.Length
5.4.4. Your table should eventually look something like that below
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FOR557 – 04
Exercise 5_04
Heads Up Digitizing
Due: 11/5
6. The store lot GPS coordinates are:
• 1114336.45, 1363137.06
• 1114604.72, 1362144.72
• 1114597.05, 1361761.49
• 1114321.12, 1361746.16
7. Use help and module 5 to create the GPS poly for the store
8. Now make a nice map showing
8.1. the roads, Classified by owner
8.2. the houses,
8.3. the farm fields, Outline only, with owner name
8.4. the river and
8.5. the Store (outline only)
9. A nice map has
9.1. A border around all the map elements (5 pts)
9.2. A legend with a neat line and with elements of the legend a distance from the neatline (5
pts)
9.3. A N arrow
9.4. A scale bar – no weird values like 123.456 feet (5 pts)
9.5. A title (5pts)
9.6. A description of the purpose of the map (5 pts)
9.7. Authors name and date(5pts)
9.8. A balanced composition with out too much or too little white space or gigantic N arrows,
etc. to take up space, with a good symbolization scheme (not a garish map)
10. The added document must summarize the results of the analysis
GRADUATE STUDENTS must locate an alternative site for the store somewhere within the 4
images. It must have the same area but as the store poly and must be roughly rectangular in
shape. Maybe you can find a site that does not take any Ag lands. Justify your choice and map
it.
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FOR557 – 04
Exercise 5_04
Heads Up Digitizing
Due: 11/5
Who Knows
Hough Long.
Otis Dimwitte.
Eustis B. Nifkin
Eustis B. Nifkin
Pete
Moss,
Esq.
Dr. Y.
Killum
Figure 1
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