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When you symbolise a layer in ArcMap, the symbols are ordered from low value to high value by default. Is that necessarily "correct"?

I've never officially studied cartography - is there a convention on whether to order items from low-to-high or high-to-low in a legend? Are both ways correct?

Edit: here's a screenshot of the symbology dialog in ArcMap, showing median weekly rents. It's ordered from low-to-high by default, but has the option to flip the order:

enter image description here

Here's how it appears via ArcGIS Server on a website:

enter image description here

Note that my question is about cartographic standards in general, and is not limited to ArcMap.

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Can you provide a picture for non-ArcMap users? –  blah238 Jun 17 '11 at 1:08
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Regardless of platform, regardless of rules, there will always be a case to break a "rule". Cartographically, what makes sense is more important than what is in the rule book, which doesn't exist, by the way. –  Dan Patterson Jun 17 '11 at 2:52
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"Rule" exists to allow a standardization in implementation...but as Dan mentioned, there will always be a case to break the rule. If it makes more sense to your users to see the symbols appear high to low, do it! Afterall, it's the end user who's more important here :) –  ujjwalesri Jun 17 '11 at 5:17
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A good book to read is "how to Lie with Maps" amazon.com/How-Lie-Maps-Mark-Monmonier/dp/0226534219 which tangetially touches on your question. In the same way you chose the colours, the order you display them in will convey different messages. If your client is an estate agent, high rents would be at the top and prominent. If you've got a website aimed at cheap accommodation, the reverse will apply. –  MerseyViking Jun 17 '11 at 10:01
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Tend to use High Top of Legend and Low at the Bottom - This can be done in ArcMap by select all the ranges and right clicking and reverse order. - this should be the same on the legend as long as it is dynamic. –  Mapperz Jun 17 '11 at 13:49
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I don't have any classical training on map making and this is just my 2 cents, but from a usability standpoint, I would think that you would want the most important/informative class listed first so that viewers will be drawn to that. It's tricky though since single classes won't mean much without the context of the others. Mersey, thanks for the tip. I'm looking forward to reading that book!

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