Lab 3: I’ve Got Isarithm
In this lab, you’ll create a small multiples layout of isopleths (with or without isolines) to get used to
working with rasters in Illustrator and the small multiples layout to show change.
Data collection and preparation
For the isopleth, you will need point data with a “volume” value. This could be temperature data,
precipitation, number of doctors in a hospital, elevation, etc. You will either need data with some way
to represent it spatially, so either X-Y coordinates, or a field to join it to an existing point file (e.g. city
names), or continuous raster data, such as a DEM. With interpolated data, this often means
downloading a table of point features with coordinates (such as weather stations), and then a table of
volume data, and stitching them together first. MS Access is a great tool for that sort of clean up.
For this lab, you’ll be doing small multiples (4-5 maps), so you’ll need a data set that exhibits change,
such as population over time, or seasonal climate data. A tutorial for retrieving info from the National
Climate Data Center has been uploaded, and the National Historic GIS (nhgis.org) will give you access to
all years of the US census. Other data sources are also possible, but leave time to work on the map!
Part 1: Isopleths
1. Project your data frame before manipulating any data
2. Interpolated data:
a. Bring your point data into ArcMap (joined to cities, or plotted on x-y coordinates.
b. Spatial Analyst Tools > Interpolation (make sure the SA extension is enabled).
c. Select an interpolation method (IDW, Kriging, Spline or Natural Neighbor). Try them all
to find the best result for your data. Don’t forget to set your processing extent larger
than your subject area to avoid blank spaces.
3. Raster data:
a. Bring your DEM into ArcMap
4. Trim your raster to the shape of your subject area using SA Tools > Extraction > Extract By Mask,
or Data Management > Raster > Raster Processing > Clip
5. Once your raster is created, classify with an appropriate Defined Interval or Stretched values,
and represent with a suitable color ramp.
Part 2: Isolines
1. Use SA Tools > Surface > Contour to create contour lines at an appropriate interval from your
DEM or interpolated surface
2. Select an index contour value and symbolize the contour lines appropriately.
3. Add a field to the table called ContourType and set all of the index contours to Index.
4. From the Customize Menu, select Extensions, and turn on the
Maplex extension.
5. Add the Labeling toolbar and select Use Maplex Label Engine
from the Labeling menu.
GSP 416 – Lab 3: Isopleths
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6. In the Layer Properties, on the Labels tab, select Define classes of features and label each class
differently.
7. Uncheck the box “Label features in this class” for the Default class.
8. Click Add and enter Index as the Class Name. Click OK.
9. Click SQL Query, and enter a query that will select just your index contours.
10. Set up your symbol properties as usual, and verify that only your Index class will be labeled.
11. Click the Placement Properties button. Under Label Position, click the Position button. (Feel
free to look around at all the options while you’re here.)
12. Select Centered Curved and click OK until you are back to Layer Properties.
13. Check Label features in this layer and click OK.
14. Convert the labels to annotation to get them where you want them, or turn off labeling and use
the individual labeling tool (Drawing toolbar) to place labels that inform but don’t interfere.
Moving to Illustrator
This process will involve multiple exports to get data in the best format, so before you begin, zoom to
the extent you want and set a Bookmark.
Tips:


Raster data and some fine-grained vector data will become slicey images in Illustrator if you
export the whole map as one, so export them separately (as TIFFs to avoid slices), and then
export your vector layers.
Remember, text will import to Illustrator as 1pt font until you move it. So, move it before
editing.
What to turn in
A map using isopleths and isolines in a combination which enhances the readability and visual impact of
the data. Map should be 11x17, in PDF or JPG format.
In the submission box, address the following:
1. Briefly describe your data set, where you got it and the process needed to make it useful.
2. Which interpolation method did you use, and why?
Be prepared to share some of this information during the critique process also.
GSP 416 – Lab 3: Isopleths
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