Reading Old Maps and Atlases

Why maps and atlases help

A map shows where things were, in relation to each other, at one moment. An atlas gathers many sheets into a volume, often at a larger scale, covering a city or county lot by lot. For local historians they answer questions that words struggle with: where a street ran, what stood on a corner, how large a factory was, where the river bank lay before it was filled in.

They are not neutral pictures. Each was made by a publisher for a purpose, at a particular date, using the best information the maker had, and that shapes how it should be read.

Types you are likely to meet

County and city atlases. Published commercially in the nineteenth and early twentieth centuries, these show streets, blocks, property lines and often owners’ names. Some were sold by subscription to property owners, who might pay to appear in the book.
Fire insurance maps. Made for insurance underwriters, these show the footprint of each building, its construction, number of stories, and uses such as dwelling, store or factory. The best-known are the Sanborn maps, which many libraries hold in print or digital form.
Early surveys and manuscript maps. Drawn for land division or boundary disputes, these are individual documents, and colonial maps and surveys require different handling from printed atlases.
Topographic and government maps. Produced by public agencies, these show terrain and water as well as built features.
Transportation and utility maps. These show rail, ferry, trolley or water-line routes.

Each type answers different questions. Combining them is usually better than relying on one.

Reading the scale

The scale tells you how the map relates to the ground. It appears in one of several forms:

A bar scale, a drawn line marked with distances. It survives copying and enlarging, so it is the most reliable, because it changes with the image.
A ratio, such as one unit on the map equals a given number of the same units on the ground.
A statement, such as a certain number of feet to the inch. Fire insurance maps commonly used 50 feet to the inch for urban sheets, though you should check the sheet in front of you.

A statement or ratio is accurate only for the original size. If a sheet has been reduced, photocopied or displayed on a screen, use the bar scale or measure a known distance, such as a standard block, to calibrate. Atlases may also use different scales on different pages, which the sheet will indicate.

Reading the legend and colors

Legends, keys and notes explain the symbols. Do not assume they match those of another publisher. On many fire insurance maps, colors indicated materials: for example, one color for brick, another for wood frame and another for stone, with different styles for fireproof construction. Abbreviations marked uses such as dwelling, stable or store. Because conventions varied and changed between editions, read the key printed in that volume.

Pay attention to what is symbolized. Windows, chimneys and outbuildings may be shown schematically. A rectangle labeled with a name does not necessarily show the building’s exact shape.

Dates and updates

Many atlases carry a date, but the information may be older than the date suggests. Publishers reused plates from earlier editions and revised only part. Fire insurance companies kept volumes up to date by pasting small printed corrections over old areas. In surviving copies you may find several layers, so the sheet shows the latest correction, not the original survey. Libraries that have scanned these maps sometimes capture the layers separately or note the date of the last correction.

To work out what a sheet really shows:

Check the title page and the date of publication.
Look for a survey date or revision date on the sheet.
Look for paste-overs or hand corrections.
Compare with the same sheet in earlier and later editions.
Cross-check with other records, such as dated photographs or listings in city directories.

If features that you know existed are missing, the sheet may predate them; if features known to be demolished still appear, the sheet may not have been updated.

Comparing editions over time

One of the most useful techniques is to place editions side by side. A block that holds houses on one sheet and a factory on a later sheet tells a story of changing land use. Look at:

changes in street names or the opening of new streets;
shifts in the shoreline, wharves and filled land;
the arrival of rail lines and industrial sites;
lots subdivided or combined;
large buildings replaced by smaller ones, or the reverse.

Observations like these give visual depth to broader accounts, for instance the growth of industrial Camden or the changes of the waterfront. Be careful not to treat a gap between editions as the date of a change; a change may have occurred at any time between surveys.

Finding owners and tying maps to deeds

Some atlases print owners’ names on lots, and these can lead to deed records and to census records that identify the family. The name on a map shows who was said to hold the lot when the map was prepared, which may differ from the current owner or the occupant. Treat a map owner’s name as a lead.

Cautions

Accuracy varies. Commercial maps could contain errors, simplified boundaries and planned streets that were never built. Proposed subdivisions sometimes appeared as though already existing.
Purpose shapes content. Promotional maps might exaggerate prospects. Insurance maps concentrated on risk, so they may show less about landscape and open ground.
Names and numbers changed. Street names and house numbers were sometimes revised, so match with care.
Digital overlays are approximate. Georeferencing, which fits an old map to a modern one, is useful but never exact, and old maps may distort at the edges.
Maps omit people. A building footprint says little about who lived or worked in it.

Handling and access

Original atlases are large and fragile. Use scanned copies when you can, and follow the library’s handling rules for originals. Many collections are now online, though access, resolution and rights terms differ, so check the holding institution for current information.

Recording what you find

Note the title, publisher, date, plate or sheet number, scale and the specific lots or features you studied. Record the edition and any visible corrections. Save screenshots or scans with the citation attached, so the observation can be checked later by anyone who sees your conclusion.