Size Matters: Why Do We Measure the Size of Maps, and How?
/So, my colleagues in the map library are having an ongoing discussion about how to measure maps. I thought this was a simple act, and I was ready to add my ten cents’ worth (or should I say my half-a-centimeter’s worth?). After all, I’ve long carried around a sewing tape in my pencil bag, so I can measure maps at the drop of a hat, no matter which library I’m in.
But then I learned not to be so self-confident: measuring the size of a map turns out to be really quite complex.
There’s a philosophical question (how do we construe this thing that we need to measure?), the question of precision (how finely do we measure?), and a pragmatic question (what use is to be made of whatever measurements are recorded?), all of which influence the selection of which part(s) of an image are to be measured. Add to that a great deal of historical inconsistency in practice, and the question becomes difficult to answer.
I’m not going to come to an answer. Rather, I just want to review the basic issues.
What’s Generally Accepted
A few things are mostly accepted. It’s a widely accepted convention—although not always followed in the past, nor even in the present day—that we specify dimensions as height by width. Typographically, it is best not to use the letter “x” to separate them, but rather to use the mathematical sign for multiplication, “×” (Unicode U+00D7). If the thing being measured is a circle or a sphere (a globe), then one specifies the diameter, often prefaced with “⌀” (diameter sign, Unicode U+2300, although I think most people use the upper-case Scandinavian letter “Ø” which is Unicode U+00D8). The units used in measuring maps have generally been Metric (variously millimeters, centimeters [common], or meters, as seems appropriate to the magnitude of the map); in the past, Anglophone map scholars used inches or feet, but standard practice for several decades has been to use Metric measures.
There are also six pairs of dimensions that one might measure off a map. Terminology does vary somewhat; in the following I use these terms:
• item – i.e., the largest dimensions of the support (vellum, paper, stone, etc.) that bears the image, often known as “sheet size” but this term properly applies solely to a single paper support;
• folded – i.e., the largest dimensions of the support when folded (if the support is folded);
• plate mark – i.e., for copper-engraved maps, the dimensions of the deformation to the support caused by the printing surface (copper plate);
• neat line – i.e., the frame, usually rectangular and perhaps decorative, that holds in and surrounds the map content;
• map – i.e., the largest dimensions of the “map” image as opposed to the “non-map” elements, which might be the same as the neat line, if present;
• image – i.e., the largest dimensions of all the elements of the work, map, decorations, text, etc., also known as the print area for printed works.
All of these sizes are complicated for maps assembled from multiple supports, like a large wall map, especially when the individual supports were not actually assembled, or assembled and then dissected for mounting on cloth. Whenever possible, when publicizing map dimensions, one should always specify which dimensions were recorded.
The Philosophical Question
The philosophical question is this: we have a map in front of us; are we treating it as a repository of information or as an object?
The former position is that of the map librarians who have established cataloging standards over the last century or so. From this perspective, what is of interest is the extent of the part of an image that holds the content. We can thus find comments in various cataloging rules that one must measure to the inside of the neat line (which might be significantly thick). According to such standards, the dimensions to be recorded are the neat line or, if no neat line, then the map area.
The latter position is that of scholars like myself who are interested in the entire image, including all the “marginal” “decoration” and text that surround the map proper. That is, the dimensions should be of the image area, which may or may not be of the neat line.
Here’s an example of the difference. In this bird’s-eye view,
a map cataloger would give the basic dimensions as those of the rectangular neat line of the image. By contrast, in describing this map, I would include the extent of the text below the view/map that is an integral element of the item (giving not only title and imprint but also an index to the key features of the view/map).
Plainly, when giving dimensions, one must be clear about which dimensions one is specifying and, if appropriate, to record multiple dimensions.
The Matter of Precision
How finely does one measure? When British and US bibliographers used inches, they might record a dimension to the nearest fraction of an inch as defined on their ruler, even to a sixteenth of an inch (1.587mm). Metric rulers generally measure slightly more precisely, to one millimeter.
But is it worth it? The rule of thumb that I was taught as a student, by David Woodward and others, was that measuring to 1mm was false precision: over the life of a map, temperature and humidity changes mean that the support will expand and shrink; the precise degree and pattern of physical change is unique to each work. Furthermore, if the map was printed from a copper plate by means of a high-pressure intaglio press, then it would have been distorted at the time of impression. In this respect, rounding to the nearest 5mm (0.5cm) gives an appropriate degree of precision when comparing items that have had different lives.
I have seen some guidelines specify measurement to the nearest centimeter, but for commonly sized items that seems just a bit too crude. On the other hand, if one is working with a large item, several meters in either extent, then maybe a centimeter is appropriate precision.
The Pragmatic Question: Why?
And then there’s the big question: why measure map dimensions at all?
Digital imaging. One thing that I had not actually realized until the other day was that the darkroom gods who create digital images of maps are interested in recording the size of the specific object that they are imaging, at the time it is imaged, so that an image might later be reproduced at the same size as the original. So, before taking a digital picture with their multi-mega-pixel cameras, they measure the dimensions of the entire item to the millimeter and record it in the technical metadata that will be embedded within the digital file. One can access this information through the software you use to view and edit such files (Photoshop, Graphic Converter, etc.) This all makes sense: they record the size of the item at a particular moment in time, not as it was two years previously, or will be two years hence, and not with the intent of comparing this item with other items.
Cataloging. Library catalogs serve several purposes, not least keeping track of all the items in a collection. Catalogs also guide users to the items (they think that) they want to read (and perhaps to guide them to the items they need to read). A key set of information about each item records its physical form, necessary for discerning and differentiating between items, for treating items (shelving and finding), and for giving an idea of the nature and relevancy of the item.
For maps, size is really useful in assessing the potential usefulness of a map: a large map of, say, France will hold much more information than a smaller one. In this respect, it makes sense for catalogers to record map (or neat line) dimensions. At the same time, the physical description in the catalog is used by librarians to place the item in appropriate shelving, drawers, or cabinets; in this respect, the key dimensions are those of the item as a whole. That is, from a librarianship perspective, it’s best to measure both map (neat line) and item dimensions. Given that it is possible for the map to change size while in storage—although it is to be hoped that modern storage systems maintain a consistent climate—it is best to round measurements to the nearest half centimeter.
Curatorial. A further element needed for curatorial work is the size of the margins between the image and the edge of the item. This is key information when a preparator is assessing how to frame an item for display: is there enough space for a mat, or will the item need to be floated within the frame? Preparators of course work to the millimeter in working with individual items.
Bibliographic. The function of bibliography is to position a work in relationship with other, related works. “Work” might vary from an individual impression (when bibliographers study all surviving impressions pulled from one printing surface) to an entire series of editions. Dimensions are crucially important in terms of being able to differentiate between works.
And this is where my brain gets confounded. Depending on the nature of the work, all the dimensions are potentially important. It’s generally held that item size is irrelevant, given that the support can be trimmed down or enlarged with paste-ons. But then there are some works in which impressions were pulled on both plain, small sheets and on fine, large sheets with large margins; such differences should be recorded. The careful bibliographer will measure and record all relevant dimensions. Given that the need is to compare multiple works against each other, precision should be 0.5cm.
Reproductions in print and on screen. A key problem for scholars is that maps are generally shrunk, sometimes enlarged, to fill pages in a book or article or the screen of a monitor or tablet. In such circumstances, it is absolutely necessary in captions and metadata to provide the key dimensions of a work so that people don’t make mistakes about the nature of the items they see reproduced. In my personal practice, I assume that dimensions are for the image unless otherwise specified, but it’s probably always best to specify explicitly the dimension being provided. The function is to give the reader or viewer a sense of scale, so precision to 0.5cm is appropriate.
Summary
Digital imaging :: item dimensions, recorded in the technical metadata :: to nearest millimeter
Cataloging :: map dimensions on item dimensions folded down to fold dimensions :: to nearest 0.5cm
Curatorial :: image dimensions on item dimensions :: to nearest millimeter
Bibliographic :: conceivably all dimensions :: to nearest 0.5cm
Reproduction :: image dimensions :: to nearest 0.5cm
