Alt text for maps, site plans and plats

What alt text does in a planning packet

Alt text is the short written stand-in for an image that a screen reader reads aloud. In a planning packet, the images often carry the decision: where the parcel is, what it is zoned, where the driveway goes. WCAG 2.1 success criterion 1.1.1 asks that every image that carries information has a text alternative serving the same purpose.

The W3C explains the rule in Understanding 1.1.1: Non-text Content, and shows how it is done in a PDF in technique PDF1, which stores the text in the image’s Alt entry. You rarely touch that entry by hand. Word and Acrobat write it when you fill in the alt text box.

The hard part is not the software. It is deciding what to write for a zoning map or a 40 page plan set, and that is what this guide is about.

A short alt text plus a longer description

Maps, site plans, plats and charts hold too much for one sentence, so the W3C calls them complex images and asks for two parts. The short alt text names the image and says where the details are. The long description, written as normal text or a table, gives the facts a reader needs.

The W3C complex images tutorial describes this approach and adds a point that suits staff reports well: make the long description available to everyone, as part of the main content. Most staff reports already describe the site in words. The job is often to make that text complete and to point the alt text at it.

A good long description answers the questions a resident would ask while looking at the image:

• What is shown, and where is it?
• What does the decision turn on: zoning, size, access, setbacks, height?
• What changes if the item passes?

It does not need to describe colors, line weights or the legend, unless those carry meaning that the text does not.

When an image is decorative

An image is decorative when it adds nothing the text does not already say. Borders, divider lines, background textures and a town seal printed beside the town name are decorative. They should be hidden from screen readers, marked as artifacts in a PDF or as decorative in Word, rather than given alt text.

The W3C decorative images tutorial lists the common cases, including images “identified and described by surrounding text”, and notes that only the author can judge an image’s purpose. In a PDF, W3C technique PDF4 hides decorative images with the Artifact tag. In Word, right-click the image, choose View Alt Text, and select Mark as decorative.

Be careful with the word decorative. A photo of the site is not decorative just because the report describes the site elsewhere, unless the description really covers what the photo shows. When in doubt, the W3C alt decision tree walks through the choice.

A worked example: one rezoning packet

Here is a worked example from a made-up town we will call Anytown. The planning commission is hearing a request to rezone Parcel 7, a generic 3.1 acre lot on Mill Road, from Agricultural to Single Family Residential. The packet has seven images. Below is what we would write for each one.

1. Vicinity map. Alt text: “Vicinity map showing Parcel 7 at the northeast corner of Mill Road and County Road 12. Described in the Location section.” The Location section then says what is nearby: the elementary school half a mile west, the creek along the north edge.

2. Zoning map. Alt text: “Zoning map of Parcel 7 and surrounding land. Described in the Existing Zoning section.” Long description: “Parcel 7 is zoned A, Agricultural. Land to the north and east is also zoned A. Land to the south, across Mill Road, is zoned R-1, Single Family Residential. Land to the west is zoned C-2, General Commercial.”

3. Site plan. Alt text: “Proposed site plan for Parcel 7 with 11 home lots and one new street. Described in the Proposal section.” The Proposal section lists the new street and its single access onto Mill Road, the lot sizes, the detention pond in the northeast corner, and the setbacks.

4. Plat. Alt text: “Preliminary plat of Mill Road Subdivision, 11 lots and one tract. Lot table follows.” Then a real table with a header row: lot number, area in square feet, frontage. Street names and easements go in a short list below it.

5. Elevation drawing. Alt text: “Front elevation of a typical home: two stories, pitched roof, attached two car garage, 28 feet to the ridge.” Height is the fact a neighbor cares about, so it goes first.

6. Site photo. Alt text: “Parcel 7 seen from Mill Road looking north: an open hay field with a row of cottonwoods along the east edge.” Say which way the camera faces, because a photo of a site is often used to show views.

7. Town seal. Printed next to the words “Town of Anytown” in the report header, so it is decorative. Mark it as an artifact.

The north arrow, scale bar and legend inside each map do not get their own alt text. They are part of the image, and the facts they carry belong in the long description.

Charts in staff reports and budgets

Charts follow the same two-part pattern. The alt text states what the chart is and its main point, for example that building permits rose each year from 2022 to 2025. The numbers go in a real table next to the chart, with a header row, so a reader can check every value.

The W3C complex images tutorial uses a bar chart as its main example and suggests summarizing the chart in the surrounding text too. If a chart or map uses color to show categories, such as green for parks, also label the areas or describe them, because WCAG 1.4.1 says color cannot be the only way information is shown.

Common mistakes to avoid

The most common mistakes are empty alt text on an image that matters, a file name read aloud, and alt text that says “map” and nothing else. Each leaves a screen reader user without the fact the image was there to show. A few habits catch most of them before a packet goes out.

• Do not start with “image of” or “picture of”. Screen readers already announce that it is an image.
• Do not paste the whole staff report into the alt text. Keep it short and point to the description.
• Do not write “see attached”. Say what the image is.
• Ask applicants and consultants for a written site description with their plans. It is easier to edit than to write from scratch.
• Check scanned plan sets: if a plan is a scan, its text labels are pictures too. Our guide on scanned documents in agenda packets covers that.

For where alt text fits in the whole file, see how to make an agenda PDF accessible and the one page WCAG checklist for documents. Our free PDF checker shows whether a posted file has tags and text at all.

What we do about it

What we do about it is write the descriptions for you. Each month we find the packets your town posted, add alt text and long descriptions to the maps, plans, plats and charts, mark decorative images, and have a person check every file. The work goes into your dated Readable Record. See how it works or pricing.

This guide explains the rule in plain language. It is not legal advice. For decisions about your town, talk to your attorney.