cartography - Is there cartographic convention to ordering legend items (high-low or low-high)?

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:

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

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

Answer

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!