In this article you will learn how to calculate the geographic grid of the layout of your ArcMap files in a professional way, keeping the symmetry of the lines that represent the coordinates LONGITUDE / LATITUDE.
It used to happen to me that when generating the flat coordinate grids for the layout I would start guessing about the correct spacing of the meridians (longitude) and parallels (latitude), and I would spend a lot of time on that task trying to get a graphic output that looked a bit harmonious to the eye. However, I have seen cases where the person in charge of the geographic information system, simply assigns a spacing without paying attention to details and obtains results like the following, where no symmetry in the coordinates is appreciated:
So that you do not spend a lot of time like me or get results as in the previous example, I will show you how you can calculate the spacing of parallels and meridians with the following formulas that I devised:
Formulas to calculate the spacing of geographic grids in ArcMap / ArcGIS
X (EAST) spacing = (Right - Left)/(Number of desired divisions)
Y (NORTH) spacing = (Top - Bottom)/(Number of desired divisions)
“Right”, ‘Left’, ‘Top’ and ‘Bottom’ refer to the boundary coordinates of the extent of the visible Data Frame window in decimal degrees; save the ‘Left’ and ‘Bottom’ coordinates since you will need to specify the longitude and latitude coordinates as custom origin later on.
As you can see you will need the extreme coordinates of the Data Frame, these can be consulted in the following way:
How to query the limit coordinates of a Data Frame in the ArcMap / ArcGIS layout?
0. Make sure that the scale is set to the desired number, for example 1000000 in the “Standard” toolbar and that the view is as you want it.
1. Right click on the Data Frame (a).
2. Click on the “Properties...” button of the displayed submenu (b).
3. Go to the “Data Frame” tab (c).
4. In the “Extent” section select the “Fixed Extent” option (d). (Make sure you are using a geographic coordinate system).
Although, having obtained this information you can do the calculation with the formulas that I present in the section “Formulas for calculating the spacing of geographic grids in ArcMap / ArcGIS”, you can also download the following Excel workbook (Link)
With this spreadsheet you only have to copy the coordinates “Left” and “Right” in the cells indicated in the spreadsheet, the same with the coordinates “Top” and “Bottom”, and indicate the number of divisions in cell E8. The division calculated for latitude and longitude will be in cells E9 and E10, and the origin of the axes in cells E12 and E13.
Whatever your choice is, once you have the calculations, follow the next steps:
How to define the grid spacing for a Data Frame in ArcMap / ArcGIS layout?
1. Right click on the Data Frame (a). Click on the “Properties...” button of the displayed submenu (b).
2. Go to the Grids tab (c). Select the flat grid, which if it does not have a custom name should be called “Graticule” (d) and press the “Properties...” button of this window (e).
3. In the “Reference System Properties” window go to the “Intervals” tab (f) and select the “Decima Degrees” option (g), then paste the result of the calculation in the “X Axis Interval” and “Y Axis Interval” items (h).
4. Make sure that the option “Define your own origin” is checked and paste there the corresponding result or simply write the coordinates “Left” and “Bottom” in “X Origin” and “Y Origin” respectively (i).
Result:
This is the only way of calculation that I have thought for the geographic grid calculation, it is not possible to modify the geographic extent or the scale without losing the configuration, so it is recommended for very specific uses.
I also recommend you to visit my articles for the calculation of grids with planar coordinates:
Excel GIS Measured Grid Spacing Calculation Option 1
Excel GIS Measured Grid Spacing Calculation Option 2
NOTES
- It often happens that the coordinates collide at the corners, to solve this I recommend you to place some white square type graphic elements in each corner.
- This calculation should be used only with a geographic coordinate system established in the Data Frame, if you change to a flat coordinate system the original distribution will be lost.
- The calculation is intended for a large scale, for smaller scales it may not work.
I hope you enjoyed this article, soon I will upload a video explaining the procedure that you can consult in this blog. Save my blog among your favorite links, I will be uploading many more tricks of this style, remember that you can send me your concerns in the contact page or leave your comment, I will be attentive to respond.
