Does Apple Watch 3 support Noise app

I would say you are over thinking the watch app.

Watch apps on Watch OS 2 and iOS 9 are extensions. They are the antithesis of a functioning app and simply a little detail or a little tidbit.

Furthermore, Apple approves apps that do absolutely nothing without a paid account. Netflix, Casper Focus, Splunk, all the newsstand subscriptions where you need to pay for content before reading an issue.

Now - Apple's review guidelines let them have great latitude to deny apps for no reason at all - let alone 2.12 "not very useful" which itself is highly subjective.

What you are concerned about also concerns many other app developers and it sure would be nice if there were a way to pay for "Pre-Approval of Innovative Features" so you could invest maybe 5k of effort to prototype and then pay for a review by Apple before investing the actual amount of development work in your app. See this story for the details of how pre-approval and the developers surveyed are in similar situation wondering what might pass review:

• https://www.macstories.net/stories/developers-apples-app-review-needs-big-improvements/

Unfortunately there are no apps that satisfy your needs.

The Apple Watch Series 2 can track your location using its GPS receiver, but it can't determine your altitude/elevation on its own. It's technically impossible. The GPS receiver in the Apple Watch Series 2 is not as capable as the one used in current iPhones.

You can, however, use an app like ViewRanger in conjunction with an iPhone 6, 6 Plus, 6s, 6s Plus, 7 or 7 Plus. These devices have built-in barometers that can be used to determine your altitude.

I hope this answers your question.