Mara Kestrel Booking from February 2027

7 min read

What a flood map taught me about uncertainty

People trust forecasts more when you tell them how sure you are. Showing uncertainty is a design skill, and a public duty.

A decimal point is a claim

“High tide: 5.34 m” sounds precise. The hydrologist I worked with on Tideline would only promise “probably between 5.1 and 5.6”. The decimal point was claiming a certainty nobody had.

When forecasts like that turn out wrong, people stop believing the next one.

Draw the range

We drew the forecast as a band, with a darker likely range inside a lighter possible one. In testing, residents read it correctly almost immediately, and said they trusted it more than a single line.

People trusted the range more than the number.

Make it survive the photocopier

Colour alone fails for colour-blind readers, on cheap printers and on screens in bright light. Hatching patterns carried the meaning in Tideline’s zones, with colour as a second cue.

Lead with what to do

Uncertainty is easier to accept when the action is clear. “Prepare” with a range is more useful than an exact number with no advice. Put the action first, then the evidence.

— Mara

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Mara Kestrel
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Night Ward A ward board for night-shift nurses that turns forty competing priorities into one calm list.
Tideline A public flood-warning service that shows how sure the forecast is, not only what it says.
Northline fares A fare finder that leads with the cheapest valid ticket and explains the rules in plain words.
Quire An accessible design system I maintain, where every colour pair ships with its contrast ratio.
Furrow An offline-first harvest log for small farms, designed for wet gloves and no signal.
Designing for 3 a.m. Most interfaces are designed at 11 in the morning by rested people. Some are used at 3 at night by exhausted ones. Here is what changes.
The case for fewer alerts Alert fatigue is a design problem, not a discipline problem. Four questions I ask before any notification ships.
Write the empty state first The first screen most people see is an empty one. Designing it first makes the rest of the product clearer.
Design tokens are a contract, not a palette A token named after a colour tells you what it looks like. A token named after a role tells you what it promises. Only one of those survives a redesign.
What a flood map taught me about uncertainty People trust forecasts more when you tell them how sure you are. Showing uncertainty is a design skill, and a public duty.
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