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Comment by defrost | Hacker News Reader

The triple was|is a damn fine world projection.

My favourite for "local area" usage was the old New Zealand Map Grid .. not a polyconic projection, rather a custom complex polynomial optimised to reduce grid error in toto (by multiple metrics) for the North and South Islands of New Zealand.

As a topographic grid projection it was aligned with the "spine of best fit" of the two islands, rather than stright up North|South aligned, and weighted to minimise the N|S and E|W distortion within the land region of interest as distance from the centre zone increased.

https://www.linz.govt.nz/guidance/geodetic-system/coordinate...

There were very few (three ?) in use about the world pre WGS84 .. and like many things went the way of the Dodo, the Krasovsky 1940 ellipsoid, the Bessel 1841, and all those tens and tens of other ellipsoids, datums, and projections of days yore.

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> My favourite for "local area" usage was the old New Zealand Map Grid .. not a polyconic projection, rather a custom complex polynomial optimised to reduce grid error in toto (by multiple metrics) for the North and South Islands of New Zealand.

Paper link: https://www.linz.govt.nz/resources/research/conformal-mappin...

That's the paper alright, I've got a physical copy in a filing cabinet somewhere :-)

IIRC, for anyone else looking for a curio, there was one state|county|region in the USofA that used a custom conformal projection for a local grid system pre 1980s .. somewhere outside the regular PLA mapping grids.

I don't think this is the one you're thinking of, but in NYC the subway maps (which are not particularly geographically accurate) are drawn with Manhattan vertical, rather than on its 20-something degree tilt.

> subway maps (which are not particularly geographically accurate)

Subway maps and bus maps in cities are very typically not geographically accurate map projections .. the focus tends to be on a compact stylisation that represents connections for travel plans.

Historically Roman Road maps were on a scroll and very linear, today the UK underground tube maps are displayed in a manner that aids commuters in making connections.

I'm not all that familiar with NYC subway maps (only there for a short time in the 80s .. and who can recall their youth?) but I remember them being more "graphic" rather than "geographic".

I'm thinking more of a local land projection map that would have been used for local surveying in the days prior to global GPS .. but thanks for the thought all the same!

The NYC MTA map is pretty geographic by metro map standards. There are some obvious distortions, like Manhattan being wider than it actually is and it's not actually vertical as noted before. It also includes a lot of surface street and neighbourhood references. Most metro maps just focus on station names.

Compared with something like the London Tube map or Paris Metro map it's extremely geographic.

https://new.mta.info/map/5256

Tilt relative to what? Rotating a map doesn't make it inaccurate.

My comments above were referring to the axis alignment used in a projection transformation that takes 3D points wrapped about a sphere and maps them to a flat 2D plane.

Most of the common global world projections use conic projections that have a major axis aligned NS and conic slices that are orthogonal to the cone major axis mapped to latitude lines that are East-West.

There are many other types of projections, the older NZ map grid is an unusual one.

Once a projection is used to make a flat map, that map can be rotated about in any direction .. but that's another thing altogether.

You may, or not, enjoy looking through a free USGS projection reference of note:

Map projections: A working manual Synder (1987) https://pubs.usgs.gov/publication/pp1395

The Plate 1 link is to a handy wall poster of a limited number of common projections: https://pubs.usgs.gov/pp/1395/plate-1.pdf

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