Show HN: What country you would hit if you went straight where you're pointing

This app was designed to answer my wife’s question “what country would we hit if we went straight” (generally posed while pointing her phone)

But with two additional twists:

1. It loads up historical maps from different years (right now 1 BC, 700 AD, 1000 AD, 1300 AD, 1800 AD, 1900 AD) so you can see what you would hit if you had a time machine AND you went in the direction your phone is pointing

2. Tap a country/territory for an (AI-generated) blurb on what you are pointing at

How it works: Starting from your phone’s bearing, we trace the great-circle in 200 km steps, prefilter candidate countries with bounding boxes (~5–10 instead of ~200), then check ~20 km points along each segment to catch coastlines and stop when the path first enters another country.

Great-circles (https://www.movable-type.co.uk/scripts/latlong.html) are why you can hit Australia from NYC, even though when you look at a flat map that can be hard to see.

There might be some weird stuff in the explanations, I haven’t read all 1,400 of them. If you see something weird let me know and I will update it!

The app is free and doesn’t have ads or tracking — your location and bearing are only used locally to figure out where you are and what you’re pointing at

Probably will work best if you hold your phone pretty flat :)

Thank you to André Ourednik and all the contributors to the Historical Basemaps project: https://github.com/aourednik/historical-basemaps)

Show HN: What country you would hit if you went straight where you're pointing
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I think about this sometimes, so I like the idea, but how do you define “straight” on an oblate spheroid? Great circle, constant direction (e.g. “due east”), or something else?

This question ate away at me too, and I also scratched the itch: https://mrgris.com/projects/landfall/

Specifically mine deals with what you'd hit looking across the ocean from a coast. I had long wanted to make mine an interactive app but could never fully motivate myself to do it, so congrats for shipping.

An actual straight line would be tangent to the earth at that point, so I don’t think that would work well for anything over a few hundred miles.

I went with great circles since that feels like the most “natural” straight line on a sphere — the path you’d walk if you just kept going forward without steering. You could define "straight" as a constant compass direction (I think it's called a "rhumb") -- that would look straight on a Mercator map but would actually require regular steering adjustments to maintain the bearing.