Signage, viewing distance and the seams

The resolution question answered properly

“What resolution for a hoarding?” is the wrong question, and the answer people give (300 dpi) is wrong by an order of magnitude.

What matters is the angular size of a detail at the viewing distance. The working figures used in the trade:

• Viewed at 1 m (an exhibition panel, a poster): 150 ppi at final size.
• Viewed at 3 to 5 m (a shop board, a pull-up banner): 100 ppi.
• Viewed at 10 m (a building sign): 50 ppi.
• Viewed at 30 m or more (a hoarding, a motorway sign): 20 to 40 ppi at full size.

A 6 × 3 m hoarding at 30 ppi is 7087 × 3543 pixels. That is an ordinary camera file. The image everybody panics about is usually already sufficient.

The other way to say it: build the artwork at one-tenth scale at 300 ppi, which is the same number of pixels and a document your machine can handle.

Vector artwork has no resolution at all and needs none of this. Only placed photographs do.

Legibility, and the rule with its caveats

The commonly quoted rule is 25 mm of capital height for every 3 m of viewing distance: roughly one inch per ten feet. It comes from readability research and it is a floor for legibility, not a target for impact.

The caveats matter:

• It assumes good contrast, a clear typeface and a stationary reader.
• A moving reader needs considerably more. Traffic signage standards use far larger letters for exactly this reason.
• A condensed face at the same cap height is harder to read.
• Reversed type on a dark ground needs a slightly heavier weight at distance.

So: 25 mm per 3 m as a minimum, doubled for anything read from a moving vehicle, and checked by printing a sample letter and walking away from it. That last test takes five minutes and settles every argument.

Panels and seams

A hoarding is almost never one piece. Flex or vinyl comes on rolls of a limited width (commonly 1.6 m, 2.2 m or 3.2 m), so a 6 m banner is printed in panels and welded or overlapped.

Find out where the seams fall before you design. Then keep off them:

• Faces, especially eyes and mouths.
• The logo.
• Any text.
• A precise geometric alignment that will visibly step at the join.

Two or three questions to the fabricator (roll width, seam position, overlap or weld) and you can place your elements in the panels rather than across them.

Substrates and finishing

• Flex / PVC banner: the standard hoarding material. Needs eyelets every 500 mm or so and a hem (a folded, welded edge) for strength. Add 100 mm of extra material all round for the hem, and keep artwork out of it.
• Mesh: perforated, for windy sites and building wraps. Passes wind, so the image is seen through holes and loses about 30% of its density; design for it.
• Self-adhesive vinyl on ACP: shop boards.
• Foam board / Sunboard: interior only, light, cheap.
• Backlit flex: translucent, for lightboxes. Colours behave differently with light passing through them; ask for a sample lit from behind.

The things that are not your job but are your problem

• Wind loading on a large sign is an engineering question and a legal one in many places. Not your decision, and worth asking about, because a sign that comes down is everybody’s problem.
• Planning permission and local rules on sign size, illumination and position exist in most jurisdictions and vary enormously. Ask the client whether they have it; do not advise on it.
• Installation access: a sign 8 m up needs a ladder, a scaffold or a cherry picker, and the cost of that can exceed the sign.

What to send

1:1 if the RIP takes it, otherwise 1:10 with the scale in the filename. Vector for everything except photographs. CMYK, with a profile if the shop names one. Bleed of 25 to 50 mm rather than 3 mm, because large-format trimming is coarser. Hem and eyelet allowance marked on a separate layer. And a low-resolution reference JPEG so the operator can see what it should look like.