Coastal Position

Variable COAST of ten · scored for every 1 km site

Land beside the sea is worth more than the same land ten kilometres inland — and worth nothing at all if the sea is coming for it.

Eight of the ten variables measure what ground can do: grow, carry traffic, hold water, yield minerals, house people. None of them could see the thing that makes a dry headland above a bay worth more than a better farm behind it. A dry coastal tile and an inland tile with the same farmland, roads and water scored the same, and the coast read as the weakest ground in its region for lacking what it was never meant to have.

Coastal position is that missing measurement, built from two facts and nothing else: how far the sea is, and whether the sea is projected to stay where it is.

What it measures

The distance from the centre of a 1 km site to the nearest ground the sea covers today, and whether the highest projected sea-level scenario at the end of the century leaves the site dry. Both come from the same model that produces the sea-level view beside the Index, so the shoreline the score is measured from is the one the map draws.

The gate, and why it is not the score

It is tempting to score coastal land on elevation alone — high enough to stay dry, score high. That carries almost no information. In one Pacific canton of 1,572 sites, 1,546 sit above the highest projected reach; a score built on “not flooded” would separate twenty-six sites from the rest and say nothing about the rest, which is where all the ranking happens.

So elevation is the gate, not the signal. It decides whether a coastal site is allowed to have a coastal position at all. Distance is the signal.

How the number is built

The sea today. The sites the sea-level model classifies as submerged under the lowest scenario at the earliest decade — wet now, not projected to be. Their edges are the shoreline.
Distance. From the site’s centre to the nearest such site, in metres. A site on the shore scores 100; the score falls in a straight line to 0 at five kilometres inland.
The gate. If the highest scenario at the latest decade reaches the site, it scores 0 whatever its distance. It is coastal and drowning, and that is a fact about the ground, not an absence of one.
Beyond the band. Past five kilometres a site has no coastal position. Not zero — none. The Index is a weighted mean over the variables a site has, so inland ground is scored on the other nine exactly as it was before this variable existed. Nothing in Iowa moved.

What scores zero

Coastal ground the highest projected scenario reaches by the end of the century. And, as a limit, ground exactly five kilometres from the shore.

What is not measured

Views, beach frontage, resort value. A site a kilometre from the sea on a bluff and one a kilometre from the sea behind a warehouse score the same. The variable measures position, not prospect.
The front row. At 1 km resolution the score can tell the shore from one site back and two sites back, and not much finer. The premium real markets attach to the first hundred metres is inside a single tile and invisible to it.
Lakes. The shoreline is the sea’s. A great lake, however large, does not give the ground beside it a coastal position; its water is counted where it belongs, in the Water Resource Index.
Storm surge, erosion, salt. The gate is permanent inundation under a named scenario. Hazard exposure is its own variable and is reported in its own terms.
The legal shoreline. Where a public foreshore ends and private title begins varies by country and by coast. Nothing on the map is a statement about it.

How to read the score

100	A dry site on the shore.
~80	A dry site about one kilometre inland — the first row behind the shore at this resolution.
~50	A dry site two and a half kilometres from the sea.
0	Coastal ground the highest scenario reaches; or the edge of the band.
—	Inland. No coastal position, and none implied.

Ground published before this variable existed was scored on nine and says so: its model version is stamped on every tile and printed on every study, and those numbers stand as the answer that model gave.

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