Tidal atlas¶

A regional sequence of charts predicting tidal-current direction and speed by tidal hour, using arrows, rate annotations, spring/neap values, and slack-water markings relative to a named reference port or phase.

Version: v1 · 2026-09-28 · History
Domain-specific #: 12550
Domain group: Natural Sciences
Origin domain: Marine Science & Oceanography
Subdomains: Tidal Streams, Nautical Charting → Marine Science & Oceanography

Core Idea¶

A tidal atlas or tidal stream atlas is a set of regional charts used to predict tidal-current direction and speed. A typical atlas has 12 or 13 panels centered on successive tidal hours. Arrows show flow direction; length and thickness indicate approximate strength, and numbers may give more precise rates. Slack areas can appear without arrows or with a label.

British Admiralty atlases commonly report rates in tenths of a knot, with paired mean neap and spring values at a marked point. The tidal hour is a phase interval—typically half an hour before to half an hour after its labeled hour—relative to a reference-port high or low water, not simply a civil-clock hour. Users must match the reference event and interpolate the spring-neap state. Wind, atmospheric pressure, river discharge, bathymetric change, and local eddies can make actual currents differ from the prediction.

Structural Signature¶

Sig role-phrases:

coastal spatial domain. Defines the charted waters, coastline, hazards, and observation points. Constitutive map frame. If altered: Rates should not be extrapolated outside coverage.
tidal phase reference. Anchors each panel to high water, low water, or another event at a named standard port. Identity-bearing time frame. If altered: Clock time alone cannot select the chart without tide timing.
hourly chart sequence. Samples the cycle in 12 or 13 phase-centered panels. Constitutive temporal model. If altered: One current arrow is not an atlas.
current vector encoding. Uses arrow direction, length, thickness, and numeric rates to represent flow. Constitutive cartography. If altered: Symbols require the atlas legend.
spring-neap and slack qualification. Adjusts rate expectations and marks weak or reversing flow. Central operational boundary. If altered: Weather and local conditions can depart from predictions.

What It Is Not¶

Tide table. Are stream vectors mapped?
Current chart. Is the field indexed by tidal phase?
Weather forecast. Are meteorological currents predicted?
Nautical chart. Is bathymetry rather than hourly flow central?

Scope of Application¶

Use tidal atlas with edition, region, reference port and event, tidal-hour convention, date and time conversion, spring-neap factor, vector legend, rate units, and weather/local-current limitations stated.

Navigation planning. Estimates current windows.
Sailing. Anticipates favorable or adverse flow.
Search and rescue. Bounds drift scenarios.
Marine operations. Schedules current-sensitive work.
Coastal education. Visualizes tidal streams.

Clarity¶

The atlas compresses continuous space and time into discrete arrows and hourly panels. Interpolation is therefore structural, not optional, whenever a route lies between arrows or phases.

Manages Complexity¶

Prediction describes astronomical tide under modeled conditions. Meteorological and river effects can alter both rate and timing, so atlas precision should not be confused with real-time observation.

Abstract Reasoning¶

Identify region, edition, reference port, and phase event.
Convert the intended time to tidal hour.
Locate the route within the correct panel.
Interpret vector direction and neap/spring rate notation.
Adjust judgment for interpolation, weather, and local limits.

Knowledge Transfer¶

Phase-indexed vector cartography transfers to cyclic flows, but coastal tidal prediction and reference-port timing delimit tidal atlases. The nearest stopping boundary is explicit: A tide table is closest: it predicts heights and times at locations, while a tidal atlas spatially maps horizontal current direction and speed by phase. The inclusion test remains: An artifact is a tidal atlas when it presents a phase-indexed regional sequence of charts encoding predicted tidal-stream vectors and rates through a cycle. The structure no longer applies when the case exits when there is no tidal-phase sequence or the arrows describe a fixed or measured current without tidal prediction.

Examples¶

Canonical¶

For three hours after reference-port high water, a navigator selects the +3 panel, reads arrow direction along a strait, and interprets paired neap/spring rates using the legend.

Mapped back: coastal spatial domain → charted strait; tidal phase reference → reference high water +3; hourly chart sequence → selected panel; current vector encoding → arrow and numeric rate; spring-neap and slack qualification → paired values.

Applied / In Practice¶

A harbor tide table lists daily high-water times and heights but contains no regional current-vector panels. It supplies timing input but is not a tidal atlas.

Mapped back: coastal spatial domain → one harbor; tidal phase reference → high-water times; hourly chart sequence → absent; current vector encoding → absent; spring-neap and slack qualification → height table.

Structural Tensions¶

T1: compact prediction vs. continuous variability. Hourly arrows aid planning while currents vary continuously in space and time. Diagnostic: How much interpolation is required?

T2: astronomical regularity vs. weather departure. Tides are predictable while observed streams respond to wind and pressure. Diagnostic: What real-time evidence modifies the atlas?

Structural–Framed Character¶

Description turns on coastal spatial domain, tidal phase reference, hourly chart sequence, current vector encoding, spring-neap and slack qualification. Skeletal core. A repeating spatiotemporal field is discretized into ordered maps with vectors and phase anchors. Domain-bound accent. Tidal hours, reference ports, spring and neap rates, knots, arrows, slack water, and coastal routes define the atlas. Transfer remains bounded because Why not prime. Phase-indexed field mapping is portable; this is a marine-navigation artifact. The negative boundary is concrete: Any tide table, tidal-height graph, nautical chart, ocean-current map, weather forecast, current-meter record, pilot book, harbor plan, or one-time flow simulation is not automatically a tidal atlas. A tidal atlas is representational-predictive: a cyclic flow field is sampled into phase-indexed vector charts. Its character: coastal current motion made navigable one tidal hour at a time.

Structural Core vs. Domain Accent¶

Skeletal core. A repeating spatiotemporal field is discretized into ordered maps with vectors and phase anchors.

Domain-bound accent. Tidal hours, reference ports, spring and neap rates, knots, arrows, slack water, and coastal routes define the atlas.

Why not prime. Phase-indexed field mapping is portable; this is a marine-navigation artifact.

This entry is a kind of Representation.

Tide table. It supplies height and timing rather than vector fields.
Nautical chart. It supplies the geographic base.
No strict parent is asserted.

Relationships to Other Abstractions¶

Current abstraction Tidal atlas Domain-specific

Parents (1) — more general patterns this builds on

Tidal atlas is a kind of Representation Prime

Tidal atlas is a strict kind of Representation: its frozen identity entails the parent's defining structure while adding domain-specific restrictions.

Hierarchy path (1) — routes to 1 parentless root

Tidal atlas → Representation → Abstraction

Neighborhood in Abstraction Space¶

Tidal atlas sits in a moderately populated region (50^th percentile for distinctiveness): it has near-neighbors but no dense thicket of look-alikes.

Family — Domain-Specific Measurement Parameters (36 abstractions)

Nearest neighbors

Cotidal Line — 0.90
Rossby whistle — 0.86
Turner angle — 0.86
Draft survey — 0.85
Iribarren Number — 0.85

Computed from structural-signature embeddings · 2026-10-08

Not to Be Confused With¶

Tide table. Tell: Are stream vectors mapped?
Current chart. Tell: Is the field indexed by tidal phase?
Weather forecast. Tell: Are meteorological currents predicted?
Nautical chart. Tell: Is bathymetry rather than hourly flow central?

References¶

Frozen Wikipedia discovery revision: https://en.wikipedia.org/wiki/Tidal_atlas (revision 1230020851).

The frozen Wikipedia revision is discovery provenance. The retained source set was reviewed for identity, formal or operational relation, and scope. The encyclopedia's structural synthesis is bounded to those claims; a thin authority surface is recorded as a nonblocking source-strengthening repair rather than concealed.