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Help on symbolizing 1 million points

June 23 2011 | 0 comments
Categories: Symbology

I'm trying to symbolize 1 million points in PA and WV states... its turning out to be more challenging than what I anticipated. I have a field that I'm going to use to categorize symbols there are 18 categories and the count on these categories are random... they can be from 50- 400000...

Any suggestions would be great.

Mapping Center Answer:

This should not be a problem from a software standpoint, but from a cartographic standpoint, coming up with symbology for 18 different categories that your users will be able to identify easily will be a challenge. We know from research that the ideal number is much less than that -- more like 5-9 -- but if you simply MUST have 18 categories, then there are a couple of things you can consider.

From your attachment, it seems to me that the categories will all be qualitative (no magnitude message). So you want to choose symbols that will convey the message that things are DIFFERENT but not that they vary in magnitude. To do this, pick symbols that vary in shape (circle, square, star, etc...) and/or color hue (red, green, blue, etc...) Also, you can try to pick mimetic symbols (symbols that "mime" the category value), like a hand with a trash bag for "Hand pick up", because they will be more immediately deciphered. If possible use symbols that your users are already familiar with (like when we use blue for rivers and green for vegetation) -- I don't know if you can do this with the types of categories you have, but use familiarity whenever possible when you symbolize features on a map so that your users will be able to quickly decipher the meaning of those symbols.

The symbols in the Crime Mapping style that you can download from Mapping Center might give you some ideas, though I know they won't work for your specific case.

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