amergeog.org A register of how maps are made
and what they leave out Entries 001–026
Hydrography · entry 011

One river, two official courses

A channel surveyed on the ground and a channel compiled from air photographs do not agree, and neither office will call the other wrong. The register records the separation and leaves both centrelines standing.

Source scale1:24,000
MethodField / photo
StatusUnadjudicated
Open entry 011
A contour chart with a pencil and small aerial prints laid beside it

Compilation works from the sheet and the photograph together — the contour drawing on the table, the aerial prints beside it for what contours cannot say.

Latest entries

Ref · subject · method · source scale
RefSubjectMethodScaleSection
001 Where a projection is chosen before the ground is knownThe sheet's projection is often fixed by the series, not by the terrain on it. What that costs at the edges. Sheet specification Zone Projections · 3 min 006 The interval decides what counts as a hillA forty-foot interval and a ten-foot interval over the same ground produce different landscapes on paper. Levelling / stereo 1:24,000 Relief · 3 min 016 A census tract is drawn around a numberStatistical geography starts from a target population and finds lines to fit it, which is the reverse of how it reads. Statistical geography Block Boundaries · 3 min 020 Two spellings, one printedThe names register holds variants; the sheet has room for one. What the choice commits the map to. Names register Register Names · 4 min 023 Bare earth under closed canopyAirborne laser, last return, and the relict field systems that turned up under forest nobody had surveyed. Airborne laser 0.5 m grid Canopy · 3 min 008 The datum a height is counted fromEvery elevation is relative to a surface somebody chose. Readjust the network and every number moves. Levelling / stereo 1:24,000 Relief · 2 min 012 Blue lines that only run after rainIntermittent channels, the dashed convention, and how much of the network is conditional. Field and photo survey 1:24,000 Hydrography · 2 min 017 Borrowed featuresBoundaries follow rivers, roads and ridges because those were already surveyed — and inherit their errors. Statistical geography Block Boundaries · 2 min
See all 26 entries

Supported by

Practices that share our interest in how maps are made.
A gilded globe lying on charts beside a camera lens

A sphere cannot be flattened without tearing or stretching it. Every projection decides which property survives the transfer.

The six sections

26 entries in all

Projections

What each flattening keeps, and what it spends to keep it.

 5

Relief

Levelling, stereo compilation, and the choice of interval.

 5

Hydrography

Channels that move faster than the sheets recording them.

 5

Boundaries

Lines drawn around counts, and the features they borrow.

 4

Names

Two spellings, one printed.

 3

Canopy

Bare earth under closed forest.

 4

One from each section

Where to start
A hand holding a small compass over long grass Projections

Where a projection is chosen before the ground is known

The sheet's projection is often fixed by the series, not by the terrain on it. What that costs at the edges.

By the register desk·3 min read A false-colour elevation surface with contour lines threaded through it Relief

The interval decides what counts as a hill

A forty-foot interval and a ten-foot interval over the same ground produce different landscapes on paper.

By the register desk·3 min read A vertical aerial photograph of a meander loop passing through a town, black and white Hydrography

One river, two official courses

A channel surveyed on the ground and a channel compiled from air photographs do not agree, and neither office will call the other wrong. The register records the separation and leaves both centrelines standing.

By the register desk·6 min read A framed county road map hanging on a wall Boundaries

A census tract is drawn around a number

Statistical geography starts from a target population and finds lines to fit it, which is the reverse of how it reads.

By the register desk·3 min read An overhead view of a drafting desk with a lamp, dividers and a blank sheet Names

Two spellings, one printed

The names register holds variants; the sheet has room for one. What the choice commits the map to.

By the register desk·4 min read A lamplit desk with an old chart and drawing instruments Canopy

Bare earth under closed canopy

Airborne laser, last return, and the relict field systems that turned up under forest nobody had surveyed.

By the register desk·3 min read

Also supporting the register

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