Type the name of almost any island into a search engine and you will be handed thousands of maps before you have finished typing. Two of them will disagree about something basic: whether the track above the village is a road, where the ferry actually docks, if the northern beach can be reached on foot. That disagreement is rarely a mistake. It comes from different purposes, different dates and different rules about reuse. The real task is not finding a map. It is knowing, within a minute or two, whether the one in front of you is worth trusting for the job you have in mind.

Start With the Question the Map Has to Answer

A framed wall map of Sardinia and a small-craft chart of the same coast can both be accurate and almost entirely useless to each other. Before you judge a source, decide what the map must do. Are you walking, driving, sailing, planning a rental, writing a guide, or simply trying to understand the shape of a place you have never visited?

Each of those has its own failure mode. A walker cares about footpaths that turn out to be private driveways. A driver cares about roads that narrow into stairways. A sailor cares about depths quoted in fathoms where metres were expected. Naming your failure mode in advance makes the evaluation much faster, because you stop checking everything and start checking the two or three things that would actually ruin the day.

Then look for a scale statement. At 1:25,000 you can see field boundaries and minor paths; at 1:250,000 an entire island collapses into a silhouette and every cove disappears. If a map carries no scale at all, treat it as an illustration rather than a reference.

Trace the Map Back to Its Source Data

A trustworthy map can usually answer a simple question: where did the lines come from? Sometimes the answer is a national survey, sometimes a hydrographic office, sometimes a geological institute, sometimes a volunteer mapping community, sometimes satellite imagery processed by one person with a good eye and a clear method. None of these is automatically better than the others, but each has known strengths and known blind spots. A survey-grade national map is superb on coastline and place names and often years behind on new roads. A crowdsourced dataset is excellent on cafés and bus stops and occasionally optimistic about a footbridge.

For Italian islands, the national military geographic institute and regional cartography are the usual anchors; the UK has Ordnance Survey, the United States has USGS. Nautical charts come from hydrographic offices and are corrected through notices to mariners, which is a completely different rhythm from a road map revision. Knowing which family a map belongs to tells you what to double-check.

Signals of a traceable source

• A named compiler, publisher or contributing community, with a way to contact them.
• A stated edition or compilation date, separate from the copyright year.
• A legend that defines each line type instead of leaving you to guess.
• Credits naming the underlying survey, imagery or dataset.
• A changelog, version number or "revised on" note.

Red flags are equally readable. No author, no date, no legend. A coastline so smooth it looks drawn from memory. A screenshot with the browser bar cropped out. A stock-image watermark sitting quietly in the corner of what claims to be a navigational aid.

Check the Date, Then Check What Has Changed

Islands are restless places. Sand spits migrate, marinas appear, a lava flow adds new coastline, a landslide closes a track for a season. The copyright line at the bottom of a map is a poor guide to any of this, because a publisher can reissue the same data for years. Look instead for words like revised, edition or last updated, and read the small print that says which features were refreshed.

Then test the map against reality where it matters. Pick two features that would break your plan if they were wrong: the harbour entrance, the access road to the airport, the footbridge over the river mouth. Compare them with a second, independent source. If both show the same quay in the same place, you can relax a little. If they disagree, you have learned something useful about at least one of them.

Read the Licence Before You Download

Licences rarely stop you from looking at a map. They govern what you may do with the file. Public domain releases, attribution licences, share-alike licences, database licences and plain all-rights-reserved terms all behave differently the moment you print two hundred copies for a village festival, put a map inside a printed guide, embed one in a booking page, or hand a leaflet to guests.

In practice, attribution is usually simple to satisfy: a caption naming the author, the source and the licence. Share-alike terms are the ones that surprise people, because a modified map may have to carry the same licence as the original. If you are doing anything commercial and the terms are not obvious, write to the publisher and keep the reply. Store the licence text in the same folder as the file, because future you will not remember which of six downloads allowed what.

Test It Offline, on the Device You Will Actually Carry

A map that behaves beautifully on a laptop at home can fail on a phone with one bar of signal at a ferry terminal. Before you rely on it, run a few checks:

• Prefetch the exact area and zoom levels you need, then open the map in airplane mode to confirm it works.
• Check whether the app asks for a login at launch, which is precisely when you may have no connection.
• Compare the download size with the storage you have left, and keep a copy on a second device.
• Print at final size rather than judging legibility by zooming on screen; the smallest labels are what fail.
• For paper, think about the conditions: a thin laser print in a kayak hatch is not a laminated sheet.

A Five-Minute Checklist for Any Island Map Source

1. Purpose: can you state in one sentence what this map must show you?
2. Scale: is it large enough to display your smallest required feature?
3. Origin: who compiled it, and from which survey, imagery or dataset?
4. Date: when was it revised, not just published, and what was refreshed?
5. Cross-check: do two key features match an independent source?
6. Licence: what does it allow for printing, redistribution or commercial use?
7. Offline: does it work with the signal you expect to have, on the device you will carry?
8. Fallback: if it fails, what is your second option?

Keep a Small Set of Sources You Actually Trust

Once two or three good sources for an island emerge, stop collecting and start recording. Note the download date, the licence, the scale and what each source is genuinely good for: an authoritative survey for coastline and place names, a current open dataset for roads and facilities, a simple printed sheet for the field. Re-check the dates before each trip, since the marina you relied on last spring may now be a building site.

The aim is not a bigger map collection. It is a smaller one you would happily bet a full day of walking on, with the paperwork in order and a spare copy in your bag.

Photo: janeb13 / Pixabay