I think this error may be in the historical-basemaps data, because it is also present on https://historicborders.app/year/1800?lng=169.5234304&lat=-4...

Probably not scientifically accurate or anything, but if you point somewhere, then "straight" is in that direction. I guess it'll loose accuracy as you get further and further in the distance of the direction, but probably for most people would be good enough for "straight in that direction" :)

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.

The mathematical field of Differential Geometry can answer this question precisely: https://en.wikipedia.org/wiki/Geodesic#Affine_geodesics

An oblate spheroid is an example of a Riemannian manifold: a smooth object that looks like a plane (or, in general, any ℝ^n) locally, and has a way to measure angles between vectors in that local plane.

All Riemannian manifolds have an object called the Levi-Cevita connection, which defines how vectors in the local plane (tangent space) most naturally map to vectors in other tangent spaces in the immediate neighborhood.

Standing at a point on the Earth and looking in a certain direction gives us 1) a point on the manifold, and 2) a direction in that point's tangent space.

We then take an infinitesimally small step forward, and apply the Levi-Cevita connection to get from the old tangent space to the (infinitesimally nearby) new tangent space, and repeat. This defines an ordinary differential equation. Integrating the differential equation gives us a curve through the manifold.

Within some neighborhood of the initial point, this curve is a geodesic, i.e. the shortest path between the initial point and all subsequent points on the curve. This matches our typical intuition of "straight".

(Disclaimer: I am currently learning about this topic, but am not an expert.)

edit: https://en.wikipedia.org/wiki/Geodesics_on_an_ellipsoid goes into some interesting specifics about the results of this process on ellipsoids.

Love these ideas -- I've also been thinking about an "arcade" mode where you get prompted with a country "in sight" and you have to guess the bearing

Not sure what this has to do with the app.

I cannot install the app right now, but it seems to be really educational/entertaining more than just "fun", if that's fun...

Soon available for people in the Vatican as well?

> it might be worth adding awareness of things like overseas departments rather than just the parent country.

I'd guess showing the coordinates of the hit (and make it a link to maps) would be beneficial.

My aunt and uncle were disembarked from a cruise ship because they were ill (covid) and they were taken to hospital. They phoned my mum to tell her of the situation while still disoriented and said they were in Spain.

The Canary Islands are Spanish, but saying Spain in this situation wasn’t helpful when my mum was trying to book flights. Caused some mild confusion for a while.

France is the country with the most surprising shape. Most of it is in Europe but the rest covers many timezones and several continents.

So I just spent a few minutes playing with Great Circle Mapper and while it's not exactly definitive (you get a static image, no zooming) it appears that leaving from Greater London and heading in a great-circle direction toward the northeast coast of Brazil, there are indeed some combination of your location and precisely where you point the phone that you either pick up Finisterre, metropolitan France, or Brazil. I suppose if you kept going you would pick up France again as in the territory of French Guiana.

Going from, say, Land's End, it looked a bit more likely to nick northern Galicia.

Fun facts about France caused by their overseas dependencies:

- France and the Netherlands share a border. Not in Europe, where they are separated by Belgium, but in the island of St Martin

- The closest country to New Zealand is France, thanks to New Caledonia being slightly closer than Australia

- The sun still hasn't set on the French empire. It's always daytime somewhere in the French dependencies

- France's longest land border is with Brazil, thanks to French Guiana.