How can I change units of the map scale bar when the XY coordinates are in latitude and longitude degrees?

The map scale bar in is map units. This means when the map is in lat/long degrees, then the scale bar is also in degrees. You can manually change the units of the scale bar by calculating the equivalent distance in meters or feet (or whatever units you’d like).

To add a scale bar on a map:

  1. Select the map and click Map Tools | Add to Map | Scale.
  2. The scale bar is the automatically placed below the bottom axis.
  3. To edit the scale bar, click on it to select it. The properties are then displayed in the Properties window.

 To manually change the units from lat/long to meters, follow these steps:

  1. Find the center latitude of the map. You can find this with this formula:

    [(yMax-yMin)/2] + yMin

    For example, if yMin = 37° and yMax = 40.99°, then:

    [(40.99°-37°)/2]+37° = 38.995°
  2. Take the cosine(degrees) of the latitude from step 1:

    Cosine(38.995°) = 0.77720087706.
  3. Then multiply the value from Step 2 by the conversion factor for the units you want. Some common conversion factors are:
      1. km=111.3215, which is 86.5191674 for this example. 
      2. meters = 111300, which is 86502.4576168 for this example.
      3. miles = 69.172, which is 53.760539068 for this example.
      4. feet = 365228, which is 283855.521927 for this example.
  4. To change the scale bar to 100 m increments (or 100 km, 100 mi, 100 ft) change:
      1. Cycle Spacing to 100 / (value from Step 3). For example, if you wanted you scale bar to be in 100km increments, the Cycle spacing would be 100 / 86.5191674 = 1.1555813
      2. Label Increment to 100. This makes the scale bar labels align with the new Cycle spacing.

 You can set a different increment by calculating a new Cycle Spacing and entering the new Label Increment.

 You can also use the attached Excel spreadsheet as a convenient conversion calculator. For an example, please see the attached ScaleCoordinates.srf file.


Updated October 25, 2017

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