Should Legend entries be singular or plural?

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 item 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."

ArcGIS Blog post "Legend item labels – singular or plural" https://blogs.esri.com/esri/arcgis/2016/08/29/legend-item-labels-singular-or-plural/

From her post, this image shows where you should have plural legend entries. One restroom symbol implies multiple restrooms.

This is a great question. I agree that there is no standard for pluralising legend entries. Typically, I will use the singular form, but often I will make it plural. In your map, you may only have one waterbody shown. So, it doesn't make a lot of sense to call it "Waterbodies". However, I don't think it makes a huge difference, but I suppose, like anything, it depends on your audience.

Ultimately, what I put on my legends is what my client wants.

I recently have made a series of maps and the legend text was in Title Case, which is what I typically use. However, the client requested that only the first word should be capitalised. As they are paying for the maps, who am I to argue?