Should Legend entries be plural or singular?

[MatthewBuchanan]

In a map legend should the entries be singular or plural? It seems like they should be singular. i.e. Road instead of Roads. In my experience I have seen it both ways even on the same legend.

A Google image search for "map legend" lead me to conclude there is no consistent way of having a legend entry be singular or plural. The more authoritative maps I've seen have legend entries in singular. (USGS, National Geographic, etc)

So my question is, in what cases is a plural legend entry correct?

This guide says singular: http://gisgeography.com/map-elements-how-to-guide-map-making/ entry 32: Features in Legend are Present and Singular

This legend has legend categories in plural, but the individual entries are singular http://www.rootsweb.ancestry.com/~alfayett/Map_Legend.html

[DanPatterson_Retired]

not sure... USGS, National Geographic vs ancestry.com is like comparing formal vs informal, and does it matter? depends on your target audience, or... just produce a non-pluralizing category... Transportation  ... then lump in whatever you want under that category

[MatthewBuchanan]

I should not have included that ancestry.com example, that made it unclear. I'm not actually concerned about legend categories, just entries. I also forgot to include this screenshot of two different legends.

Is this completely a matter of opinion or are there some guidelines? 

Is Road better than Roads? Does Road imply only one road is on the map? I

My intended audience is engineers and geoscientists. The maps I'm making are for formal signed reports. 

[DanPatterson_Retired]

go with the singular... reason? there might only be one for a particular category (ie string bogs) and you wouldn't want people looking around for more because of the 's', hence, numerically correct even if there are more than 1.

Formal versus colloquial.

[MatthewBuchanan]

I asked Dr. Aileen Buckley, Esri Cartographer for her advice. She wrote a blog post that explains when you should use singular and plural for legend items. I asked, ”Is there a cartographic convention or guideline for legend item labels being singular or plural? Do plural labels imply something different if there are both singular and plural entries?”

In summary;

"As a rule, legend times labels should be singular nouns."...

Also, ”Do plural labels imply something different?” Yes, they do. The most common interpretation of legend item labels that are plural is that there are multiple things of the same type in a single location."

Entry on the ArcGIS Blog.abuckley-esristaff

Legend item labels – singular or plural | ArcGIS Blog 

[AbdullahAnter]

All legend entries should be singular, except the super class.

in your example , legend will be  

by the way two links that you attach in your thread is true and the are accept with what I write. 

this is the picture from plural legend as you say :

you will see that super class plural but all contents singular