The worst

To give you an idea of how poorly tree grates can look and function, here are two examples.

The round grate is the absolute worst. The whole is tinier than tiny; the metal materials jutting up from the ground are unnatural and dangerous. It's rated A1 F1.

The one with the square base is rate okay for aesthetics: I like the simplicity of the shapes and materials. But he drainage is sorely inadequate for a big tree. So I give it an A4 F1.

What are they?

Tree grates exist to protect trees from city stress, especially from potential compaction of the soil around the tree trunk. The soil needs to breath the air and absorb rainwater. The grates also protect from trash and other waste (like from dogs!) collecting around the base. Even foot traffic can be a hazard because of the high volume.
Trees have a hard life in the city. The air pollution from the cars and trucks poses the biggest threat, and I bet the sound pollution hurts them, too, but this is not proven. They get rammed by cars and trucks trying to park and by bulldozers making necessary repairs to streets and sidewalks.
Trees need to drink lots of water, with the major sources being rain and snow. Most of the water absorption comes through the roots, which typically stretch the width of the tree canopy, and sometimes even more. So most city trees are automatically at a disadvantage, just be being in the sidewalk; the total root system is rarely exposed to the elements above.

The life of the street tree is said to be 10 years, which is easy to believe, given all the stress. But the source of that statistic is one woman observing life outside her window. No really good studies exist to prove this.

Rated A10 F10--The Best

This blog will illustrate tree grates in New York City--what are they? Where are they? Why are they there? How do they work?
Discussions will be illustrated with photos and each will be rated 1-10 for function (F) and aesthetics (A).

Already I have an idea which is the best overall, and it is pictured above.

It is rated A10 because it is beautiful--round, large, earth toned, and F10 because it is designed to allow the tree to drink and grow.