Mapping tricky blocks

Surveying blocks that aren't neat rectangles — tapers, staggered ends, and irregular outlines in the Archer app.

Platform: Mobile (the Archer app)

The mark-and-fill workflow in Mapping a block assumes a fairly co-operative block: parallel rows, reasonably even ends. Plenty of real blocks aren't like that. This page covers the shapes that need extra care, and the two controls built for them.

What the fill assumes — and where the ends come from

When Archer fills in the rows between the ones you've marked, two things decide the result:

Row spacing and direction come from the rows you marked. Rows must be parallel within ±5° — that's a hard check ("rows must be parallel within ±5°"). Rows of different lengths are fine; rows pointing in different directions are not, and a genuinely fan-shaped block needs to be split into separate blocks.
Where each row starts and ends comes from the outline your posts make. Archer joins your posts into a boundary and cuts every filled row to it. So the row ends follow whatever shape you mark — straight, tapered, stepped or curved — as long as you've marked a post at each place the edge changes.

That gives you one technique for every irregular shape: mark a post wherever the edge changes. First and last rows always; then the posts along any edge that tapers, kinks, steps or bends. You're not numbering these posts — only the first and last rows get numbers — you're just giving the outline its shape.

Tapered blocks

A taper — rows getting progressively shorter along one side, following a fence line or a river — is the most common irregular shape.

A straight-line taper needs nothing beyond a normal block: mark the end posts of the first and last rows, plus both ends of a middle row (the outline always needs at least six posts across three rows), and the outline's edge runs straight between them, so the filled rows shorten evenly. Check the map after the fill — if the row ends track the real fence line, you're done.

An uneven taper needs a post wherever the taper changes rate (where the fence kinks). Mark the end post of the row at each kink; two or three extra posts is usually enough for the outline to follow.

When Archer guesses the wrong end

On a strongly tapered block, a row where you've marked only one post is ambiguous: is that post the row's start or its end? Archer makes a guess from the block's heading, and if it guesses wrong the row draws offset toward the wrong end of the block.

You can correct it directly. Tap the post to open the Edit Point dialog; on a row with a single marked post it shows a card headed Row N · this post is the… with two buttons naming the ends by compass direction — for example South end and North end (or First post / Last post if the block's heading isn't settled yet). A badge shows whether the current reading is guessed or confirmed. Tap the right one. The choice is locked: later fills won't second-guess it. The card only appears while the row has one marked post — once you've marked both ends there's nothing to guess.

Staggered starts and bent edges

Blocks whose row starts don't line up along a straight headland — staggered starts, a dog-leg boundary, a stream cut-in — are handled by the outline in the same way: mark the posts along the stepped or bent edge, and each filled row is cut to it.

If the edge is genuinely irregular from row to row (every row starts somewhere different), you'll be marking most of those posts anyway — that's the survey. Where the edge is a gap rather than an end — a road, a stream the rows resume beyond — see Mapping row breaks; the outline gives you suggested breaks for those.

A block that bends — rows on one side pointing a different way from rows on the other — is still two blocks. The ±5° check will tell you, and splitting at the bend is the right answer.

What the review dialog tells you

On a tricky block, the review dialog (Confirm outline for …) is worth reading before you hold to confirm. Besides any blockers, it notes things a mapper can act on:

"3 points off-grid (max 0.8 m, row 12)" — posts you marked that don't sit on the row grid the fill produced. Usually a post dropped at the wrong spot, or a row whose spacing genuinely changes there.
"Row 9 looks short" / "Rows 9, 10 look short" — a filled row much shorter than its neighbours. Either the outline really does cut in there, or a post along that edge is missing.
If the outline crosses itself, the status bar's sub-line says so. It doesn't block the fill, but it's a sign two posts along an edge are out of order — check the order you marked them in.

None of these stop you confirming; they're prompts to look at the map before you do.