Every digitized map, put back on the ground
Allmaps is a free, open-source tool that lays historical maps over modern ones. The process is called georeferencing. Anyone can do it in a web browser, with no GIS software and no specialist training, and once a map is georeferenced people can search it by place, compare it with today’s map, and use it as data.
What you are looking at is the City of New Haven as surveyed by A. B. Hill in about 1893, one of the Beinecke’s maps. It is being drawn right now, in this browser, straight from Yale Digital Collections’ own image server and bent to fit a modern map underneath. Nothing was exported and no copy was made.
This story uses Yale’s own maps to show how it works and what it is for. Use the arrow keys to move on. Drag the map to move around, and zoom in and out with the scroll wheel, a pinch on a trackpad or phone, or the + and − buttons at the bottom left. Hold Space at any point to see today’s streets underneath.
A picture of a map
Yale has digitized thousands of maps and publishes them through IIIF, the standard most libraries and museums now use to share images online. But a digitized map is a picture of a map. This is Amos Doolittle’s 1817 plan of New Haven, dedicated to the mayor, aldermen and Common Council: a beautiful scan, 11,483 pixels across. Yet unless you read the text on the sheet, you would not know what place it shows. It cannot be laid over today’s streets or compared with another map of the same place, and it cannot be found by searching for New Haven unless that text has been transcribed.
Georeferencing fixes that, and Allmaps needs only what we already have: the IIIF image. The next four slides show how a map is georeferenced in the Allmaps Editor.
Zoom in to see the detail of the engraving and the dedication.
Step 1: draw the mask
Georeferencing starts by drawing a mask: a polygon around the part of the scan you want to work with. The pink outline here is our mask for Doolittle. It is drawn around the Nine Squares, the original town plan at the heart of New Haven, bounded by York, Grove, State and George Streets. Only what is inside the pink line is warped; everything else is cropped away.
In the Allmaps Editor you draw it by clicking the corners on the scan. For an area like this it takes about a minute. The whole scan stays visible on this slide so you can see where the boundary lies.
Step 2: control points on the scan
Next come the control points. In the Editor the screen is split in two: the scan on the left, a modern map on the right. You click a place on the scan, then the same place on the modern map. Each pair of clicks becomes a control point: a spot on the scan matched to a location on the modern map. These two slides show the two halves one at a time.
The pink dots are the five control points placed on Doolittle’s scan: street corners around the Nine Squares. Zoom in to see exactly where each one was clicked.
Step 2: the same points on today's map
This is the other half of the Editor’s screen: today’s New Haven, with the same five control points in blue, exactly where they were clicked on the modern map. The historic map is hidden on this slide so you can see the modern side on its own.
Pink on the scan, blue on the modern map, one pair per corner. That is all the Editor needs: for a plan like this, five pairs; for a detailed survey, thirty or forty. The Editor shows the fit improving as you add them, and if a point is in the wrong place you simply drag it.
Zoom in on any blue dot to see the street corner it marks.
Step 3: the map is placed
With the mask and the control points, Allmaps warps the scan onto the modern map. Blue dots are the control points on today’s map; pink dots are where the warped scan puts them. The white lines join each pair and show the gap between where a point was clicked and where the warped map actually puts it. A short line means a good fit; a longer one tells you a point may need moving. This is the view the Editor shows you on its Results step.
Hold Space to hide the historic map and see the streets it is lying on.
Zoom in on a pair of dots to see the white line between them.
Step 4: it is published
There is no save button. Every edit in the Editor is stored at once as a Georeference Annotation: a small open file, a few kilobytes of JSON, published under CC0 at a stable web address. It records the IIIF image, the mask and the control points, nothing more. The image itself never moves; it stays on Yale’s server.
Allmaps uses that file to draw the map in the right place, and it is also what lets people find the map by searching for a place.
It always keeps the link back to the original. Alongside the Editor there is the Allmaps Viewer, where anyone can look at georeferenced maps. As in the Viewer, the strip at the top of the screen names the map and its provider. Click it, or press I, for the source information: the catalogue details from Yale’s IIIF manifest and a link to the record in Yale Digital Collections.
Doolittle’s annotation in Allmaps: annotations.allmaps.org/maps/444ba126f2bf8974 . These slides use a copy with the same control points and the mask redrawn around the Nine Squares.
New Haven, 1817
Now some more of what Allmaps can do, through six maps of New Haven from Yale’s collections, in date order. Each is georeferenced and laid over today’s street grid at the same spot. Watch the Green as you step through them: it stays put while the city grows around it.
1817. Doolittle’s plan, masked to the Nine Squares: the Green at the centre, with Yale College on its west side. Each map is shown twice: first as it is, then with one of Allmaps’ viewing features, starting with opacity, so the modern streets show where the historic ones lie.
Zoom in on the Green and Yale College.
1817, half transparent
The same map at 45% opacity, with today’s streets showing through: Doolittle’s blocks sit on the modern ones. Opacity is one of the first controls in the Allmaps Viewer: a slider you can set anywhere between the historic map and the modern one.
Not every scan has a paper colour that can be filtered away. Doolittle’s sheet is dark and uneven, so opacity is the right tool here; the maps that follow have clean paper, and for those the Viewer’s magic pen removes the sheet entirely, as the next slides show.
New Haven, 1847
1847. The Map of the city of New Haven. The city has pushed out towards the harbour and along the Mill River, and you can see the development that has followed. Forty control points.
Zoom out to see how far the city had spread by 1847.
1847, see-through
Paper removed, with the Viewer’s magic pen: nothing was edited, the colour of the sheet is filtered out as the map is drawn. Compare the 1847 shoreline with today’s: much of what is now Long Wharf and the harbour edge is filled land.
Zoom in along the shoreline to compare it with today’s.
New Haven, 1883
1883. Price, Lee & Co.’s map, surveyed by S. W. Searle for the city directory publishers. Placed with just four control points.
Zoom in to read the street names.
1883, see-through
Paper removed. The ward boundaries and the street names stay legible on the modern map. With only four control points the fit is looser in places; adding points in the Editor would tighten it.
Zoom in to see where the fit is looser.
New Haven, 1893
1893. A. B. Hill’s survey, probably the most precise of the set, with forty control points. Ward boundaries in red, parks in green, every public building named. This is the map from the first slide.
Zoom in: every public building is named.
1893, one colour
Paper removed and the drawing colorized in blue. Treated this way a historic map becomes a layer like any other: easier to read against the modern map, or you can put a second historic map underneath in another colour and compare the two. Colorize is also a Viewer setting, next to the magic pen.
New Haven, 1911
1911. The Saloon map of New Haven, made to plot where every saloon in the city stood in 1911. Eleven control points. Some of you will have seen it in the Yale Library news item about Allmaps. Open it in the Allmaps Viewer and click the magic pen to do the next slide yourself.
Zoom in on the red marks: each one is a saloon.
1911, see-through
Paper removed. Every red mark is a saloon, now on the modern block where it stood: the map stops being an illustration and becomes data.
Zoom in on a block you know and count the saloons.
New Haven, 1922
1922. The Map of New Haven and Suburbs, from Manuscripts and Archives. Ten control points. A century after Doolittle the Nine Squares are a small part of the whole.
Zoom out to see how far the city reached by 1922.
1922, see-through
Paper removed. That fixed frame of reference across maps made by different people for different reasons is what georeferencing gives you. What was on this block in 1883 becomes a matter of stepping back a few slides.
From the city to the colony
The same method works at any scale. Thomas Jefferys’s 1774 Map of the most inhabited part of New England covers a whole region rather than a city, and eleven control points are enough to lay it across three states.
Zoom out to see the whole region.
Find New Haven
Down the coast to New Haven harbour, on the same sheet. Hold Space to compare the engraved shoreline with today’s. It will not match exactly, but for a hand-drawn regional map placed with eleven points, the fit is good.
Zoom in on the harbour to compare the shoreline with today’s.
New York, October 1776
William Faden’s Plan of New York Island, dated 19 October 1776 and drawn within weeks of the Battle of Brooklyn. Its printed references mark the British and American positions.
1776, see-through
Paper removed: the 1776 positions on the Brooklyn and Manhattan of today. A hand-drawn map will not line up exactly with modern mapping, but laid over it you can see roughly where things were and compare places in a way the flat scan does not allow.
Zoom in to compare the 1776 shoreline and streets with today’s.
An old chart, straight fit
City plans are the easy case. This is a hand-drawn portolan chart of the Mediterranean from 1590, in the Beinecke’s collection: a sea chart made by and for ships’ navigators, built up from compass directions and sailing distances between harbours rather than from a grid of latitude and longitude. Its shape is recognisable, but its accuracy varies from place to place: some stretches of coast are close, others are well off.
The Editor’s default fit moves, turns and stretches the whole sheet evenly. That suits an accurate city survey, but not this chart: the gaps between the pink and blue dots show it cannot line up with all eight points at once.
Zoom in on a pair of pink and blue dots to see the gap.
The same chart, bent to fit
Same chart, same eight points, one setting changed. Instead of stretching the sheet evenly, Allmaps now bends it, like a rubber sheet pinned down at each control point (in the Editor this is the thin-plate spline option). Every point lands where it was clicked, and the coastline settles much closer to today’s. The choice of fit is made map by map and saved with the points.
Zoom in on the same pair to see the gap close.
Where the chart stretches
The same fit, coloured to show how much bending was needed: one colour where the chart had to be stretched, the other where it had to be squeezed. The stronger the colour, the more that part had to change, which gives a historian a picture of where the chart departs most from modern geography.
Zoom in to see where the colour is strongest.
Yale's maps in Allmaps
Every map on screen is one of Yale’s, georeferenced in Allmaps and drawn here together, with the most detailed maps on top. Zoom in on New Haven and the city plans, harbour surveys and an 1894 sewer plan sit stacked in place. Zoom out and you find the rest, from San Francisco to Vienna and Kunming, each still served from Yale’s own image server.
Because our maps are delivered through IIIF, none of them had to be copied or uploaded. Wherever one appears in Allmaps it carries a Yale University Library badge with a link back to Digital Collections. The next four slides show the four Allmaps apps, live.
Zoom in on New Haven to see the city maps stacked; zoom out to find Yale’s maps across the world.
Allmaps Editor
The Editor is where maps are georeferenced: the four steps you saw earlier. This is Yale’s organization page in it, listing every Yale map that Allmaps knows about. Pick any one and start placing points; there is nothing to install and no account to create.
editor.allmaps.org/organizations/yale
We have also been talking with Julia Hernández at the Beinecke about how to use Allmaps in classroom teaching with these collections.
The four steps on the 1893 Hill map, in the Editor, in one minute (recorded 17 October 2026, 1.5× speed).
Allmaps Viewer
The Viewer is where anyone can look at a georeferenced map on a modern basemap. This is the 1911 Saloon map, live. The buttons at the bottom are the controls you have seen in these slides: opacity, and the magic pen that removes the paper. The strip at the top opens the source information, with the link back to Yale Digital Collections.
Allmaps Here
Here shows the historical maps of wherever you are standing. Open it on your phone: on campus it finds our New Haven maps alongside those of other collections, such as Boston Public Library and the David Rumsey Map Collection.
Scan to open here.allmaps.org on your phone.
Allmaps Latest
Latest is a live stream of maps being georeferenced in Allmaps right now, by libraries and individuals around the world. When someone georeferences one of Yale’s maps, it appears here.
Why Yale invested, and what is next
Yale joined the Allmaps–IIIF Partnership as an inaugural Innovator-level member, and Jon Manton, Director of Digital Collections and Access, chairs its Advisory Board. Allmaps began in 2021 at TU Delft Library; the partnership, approved by the IIIF Executive Committee in October 2025, gives it a sustainable home inside the IIIF Consortium for 2026–28. Yale is listed on the Allmaps partners page .
Because our maps are delivered through IIIF, they appear in Allmaps alongside map collections from institutions around the world, and every map that someone georeferences becomes open data that serves Yale and the wider research community.
Zoom in on any of Yale’s maps around the world.
Start with a map you know
This is the 1883 Price, Lee & Co. map of New Haven. Open it in the Allmaps Editor to see exactly how it was georeferenced, or pick any map from Yale’s organization page to start one of your own.
Further reading: Yale Library’s news article on the partnership , with a short video on working with our map collection.
Questions: Jon Manton, Director of Digital Collections and Access, Yale Library, jonathan.manton@yale.edu . Every map in this story is from Yale Digital Collections; catalogue records and sources are in the Credits.