ArcMap and ArcView FAQs ArcMap and ArcView FAQs

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Back to Contour and Elevation Data​ Contour and Elevation General FAQs​
 

  • ?1) ArcMap cannot find the elevation grid after I unzipped the grid?

    Be sure to check on "use the folder names" when unzipping the grid files. Sometimes the file gets corrupted during transmission/downloading. You might try downloading the file again at another time and see if that clears up the difficulty.​

  • ?2) How do I display the grid properly in ArcMap or Arcview?

    Use the provided layer (LYR) files to load the county grids. This is a simplified legend that will allow you to view the elevation and hillside shade simultaneously. Arcview 3.2 users might not be able to load the grids into Spatial Analyst, but will be able to view the grid as an image.​

  • ?3) What is the labeling field for the contour shapefiles?

    The field named "Elevation" - Number of feet above sea level.​

  • ?4) How do I get the contour lines to display labels in meters instead of feet?

    • Right Click on the contour layer and select properties option.
    • Click "Labels" Tab and check label features.
    • Click "Expression" button and check "Advanced".
    • Paste the following code in the text box. 
    Function FindLabel ( [ELEVATION] )
         FindLabel = ROUND ( [ELEVATION] / 3.2808 )
    End Function

  • ?5) Are counties edge-matched for the grids and contours?

    All of the layers are edge-matched. The view of the elevation data is stretched to the minimum and maximum elevation for each county. To display two elevation grids together you can set the Stretch Type, under "Symbology", to "Minimum-Maximum" and adjust the elevation range to match. For some of the coastal counties you may not get valid results.​

  • ?6) What were the calculations used to create the contour shapefile and the ArcMap Grids?

    Contours shapefiles were generated from the elevation grid. The input elevation grid represented Z-values rounded to the nearest 1/10th of a foot with each cell spaced by 20 feet along the X & Y. For details on how this was generated, please read the XML metadata included with this shapefile.

    Elevation was rounded to the nearest foot by this calculation: 

    Elevation = INT(RealElevation + 0.5)

    To create the hillside shading, with 126 shades of gray, a z-factor of 3 added to 1.5 was used. This exaggerates the relief (surface) to create
    the more extreme shading. Calculation used for 126 shades:
    Hillshade = INT((HILLSHADE(Elevation,315,45,all,3) / 4) + _
                          (HILLSHADE(Elevation,315,45,all,1.5)) / 4)
     
    with Azimuth = 315, Altitude = 45, and Z-Factor = 3 and 1.5
    This location of sun is impossible in the Northern Hemisphere but is standard for hillside shading.
    Slope was resampled to a 10-foot cell spacing and rounded to the nearest 10 degrees by these two calculations:
    TempElevation = INT(RESAMPLE(Elevation, 10, BILINEAR) + 0.5)Slope = INT ((SLOPE(TempElevation, 1, DEGREE) / 10) + 0.5) * 10

  • ?7) What time of year was used for Hours of Sunshine Grid?

    Hours of Sunshine was created for 3 different times of year and 2 other grids were generated for morning and afternoon hours of sunshine. For details on how this was generated, please read the metadata included in the XML file with this grid. Below is a list of the time of year used for all of the hours of sunshine grids:

Time
  
Altitude
  
Azimuth
  
08:00
3.3
121.8
09:00
12.9
131.5
10:00
21.2
143.0
11:00
27.4
156.5
12:00
30.8
171.8
13:00
30.8
187.8
14:00
27.5
203.1
15:00
21.5
216.6
16:00
13.2
228.2
17:00
3.6
237.9
Time
  
Altitude
  
Azimuth
  
07:00
9.2
89.9
08:00
21.4
98.9
09:00
33.2
109.2
10:00
44.2
122.1
11:00
53.4
140.1
12:00
59.1
165.2
Time
  
Altitude
  
Azimuth
  
13:00
59.1
194.5
14:00
53.5
219.7
15:00
44.2
237.7
16:00
33.2
250.6
17:00
21.4
260.9
18:00
9.2
269.9
Time
  
Altitude
  
Azimuth
  
06:00
6.9
66.0
07:00
18.3
73.8
08:00
30.2
81.3
09:00
42.4
89.3
10:00
54.5
99.0
11:00
66.3
113.8
12:00
75.9
145.5
13:00
76.9
206.4
14:00
68.0
242.9
15:00
56.4
259.2
16:00
44.3
269.4
17:00
32.1
277.5
18:00
20.1
285.1
19:00
8.6
292.8
Time
  
Altitude
  
Azimuth
  
07:00
4.1
93.0
08:00
16.0
102.0
09:00
27.7
112.1
10:00
38.5
124.6
11:00
47.5
141.1
12:00
53.3
162.9
13:00
54.2
188.4
14:00
50.0
212.0
15:00
41.9
230.3
16:00
31.7
244.0
17:00
20.2
254.8
18:00
8.3
264.1
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