Geological Age Symbol Legend
I am presently working for geological mapping through ArcGIS.
(1) I need to know the easiest way to plot geological age (period) symbols both in map frame and Legend. I mean, specific age symbols like for Cambrian, Permian, and Triassic etc. need to be displayed.
(2) Is there any method to group lithologies in Legend age vise having with group lines and labels of ages?
I will be thankful to you.
Mapping Center Answer:
For the first item, you'll need an attribute in your data and then you would use Unique Values symbology.
For the second item, we did a blog entry last year that should help some as well, it's called Organizing layers with too many unique values.
This is a solution you will need to adapt to your specific datasets, and that may involve a good bit of work to come up with a standard set of attributes that can be used to drive this sort of mapping.
We've been spending a good bit of time, lately, with surface geology maps and frankly are torn about the best way to do the legends. The options are to convert the ArcMap legend to graphics and manually edit the content, which works well if you're doing a single geologic map. But if you're doing a series, especially a series that will be updated as time passes, the graphical solution doesn't provide much that's reusable. Thus, the other option is to create your legend as a dataframe, where you design a set of feature classes and features to be the symbol chips, and attributes to label the chips. In fact you'd use a data model that's very similar to the data you have in the main map.
The main issue with either approach is how much text will accompany each legend chip. If its only a little then text elements or annotation will suffice to put the rest of the text on the map. But once you start using a paragraph, the work gets harder. Most folks use word processing software to write, spell-check, and store their text. You can copy and paste the text into polygon text elements in ArcMap, or if you have lots of text and you're really doing a report that accompanies the map, then it's easier to also have the legend in another map document that you export to PDF, EMF, or AI that you can open in a graphics softare package and copy each element out and paste it into your text document.
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