The world’s single largest online collection of historical maps launched earlier this week at Old Maps Online. By the end of the year, the site aims to have 60,000 maps available for public access. Cooperating institutions include the British Library, the National Library of Scotland, the Czech Republic’s Moravian Library and the San Francisco Bay Area’s David Rumsey Map Collection. The University of Portsmouth’s Great Britain Historical Geographical Information System hosts the collection in conjunction with Switzerland’s Klokan Technologies.

Having such a large collection of cartographic history in one place and accessible by anyone with a browser is extraordinary enough. But it's not the only online map collection of note. The University of Texas’s Perry-Castañeda Library Map Collection has been a familiar online companion from the early days.

Still, what makes this project so arresting is the way the site is organized.

Starting from a map of your area, you can zoom in or reorient over a basic world map, then drill down. The right column contains a changing stack of maps germane to your area. I started, for instance, in my home state of Oregon. The stack presented me with a 1901 gazette page of the "products of selected industries" in the state and a 1935 Standard Oil road map. I spun the globe and drilled down all the way to the street level at Granada, Spain, where I had an early 20th century map of eastern Spain and an 18th century map of "Hispania Benedicta," a map of the Benedictine religious order.

Each historical map you click on is presented in a separate frame that you can enlarge, drawn from the contributing institution. A slider across the top allows you to dynamically change the offerings by moving from as early as 1000 CE up to 2010 (check Google Maps for anything more recent). A search box allows you to navigate by place name.

Everything loads surprisingly quickly given how information-dense the graphical information invariably is. But it’s a new site and not without occasional bugginess. When I traveled back to Oregon from Granada, the page insisted there was no information for this area. We’re a little out in the trees here, I grant you, but I’m reasonably sure a modern-day "here be dragons" is technically inaccurate.

Project leader Dr. Humphrey Southall told Ars, "We tried to design a very simple search interface which anyone familiar with Google Maps will know how to use, and we aim to provide instant gratification: once you find an interesting map on our site, you will be only a couple of clicks from seeing a high quality image on the relevant library's site. We are also trying to make it as easy as possible for libraries to be included: we don't try and charge them, and we aim to help them get their collections ready for us. Basically, we're aiming to include as many high quality online map collections as possible, and to make them accessible to as many people as possible."

In addition to reaching out to large academic institutions and museums, the projects are also canvassing for maps from individuals and smaller organizations. Since the maps’ copyrights are retained by the contributors, it may be appealing for collectors and small map-holding groups like local governments to contribute. Participation could increase the use of their maps and help to advertise contributors’ missions.