copyright question

Hello!

I got a threatening email from someone today alleging copyright infringement on a website that I built as a personal project back in 2013 to crowdsource the latest trail data from the long-distance hiking community. This person is an owner of a backpacking gear company which apparently owns the rights to the AT Guide, which is a popular resource of trail data among hikers. They are claiming that the part of my site which dynamically builds a PDF out of crowdsourced trail data is unfairly borrowing some visual conventions which can also be found in their guidebook.  (FWIW, I make no money from this site; it was my attempt to give back to the trail community.)

In their email, they specifically point to four aspects of the PDF which are similar to their printed guidebook. I've highlighted three of them in this screenshot. They're claiming copyright on: 1) the way of representing distances between shelters, 2) the sideways orientation of the elevation profile, 3) the icons, and 4) the convention of representing direction and distance for waypoints that are off-trail (e.g. "0.1e" = 0.1 miles east of the trail).

I'm new to copyright law. Can you really copyright such minor visual things? Their email specifically says that the "contructs [sic] and presentations" are protected by copyright. FWIW, I checked the US copyright database for the author's name (the one who allegedly has had the copyright since 2008) and nothing came up.

Since I make no money from this site, I'm reluctant to spend time/money fighting this. But if they're just trying to bully me using legal jargon (but no actual legal standing), I'd like to push back. Anyone been through this sort of thing before? Thanks for any advice!

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EDIT: This is in the United States

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