Why those units?


These are picas:


and this is a foot , or at least a part of one.


The pica and the foot have something in common. They both divide into 12 useful parts. In the case of the foot, these are inches. Inches are the units used in North America to size paper. The pica is divided into 12 points. Points are the units that typography is measured in. For example, 10 on 12 is a type specification. Ten points is the size of the characters, and 12 points is the size of the leading or line spacing.

Why should this be so? Well, North American paper sheets are sized in inches because imperial units are what the industry started with. Originally, all the paper-handling machinery built for the North American market, whether for paper making or printing, was made to handle paper to be trimmed to whole-number or whole-number fraction dimensions in inches. To change this would require retooling or replacing most of the paper-handling machinery across this continent, a terrible waste of materials and effort.

Type is measured in points because early lead typesetters had their own system of measurement. They needed a whole-number measuring system with very small units so that they could cast and set type in easy-to-reference sizes. Since lead type is no longer common, keeping this system may seem somewhat arbitrary until you consider that these type sizes have a useful relationship to imperial paper sizes.

Conveniently, point and pica measures correspond to imperial measures, so that 6 picas equal 1 inch. Because of this, picas, points and inches are easy to use together. A half-inch is 3p. A quarter-inch is 18 points or 1-1/2 picas or 1p6. An 8th of an inch is 9 points. (Picas and points are expressed <pica>p<points>, so 4p9 is 4 picas and 9 points or 4-3/4 picas.) These kinds of relationships make design and layout easier, because they help to keep measures simple and easily expressed in whole numbers and whole-number fractions.

Whole numbers

PageWhole numbers are the ones you use most commonly. They are 0, 1, 2, 3 and so on. Anything that simplifies math is welcome, and whole numbers and whole-number fractions like 1/2 are the easiest measures to work with because they simplify math. If you have a document that is 8-1/2 inches wide, the outside margin is 4p, and the inside margin is 5p6 with an 11p narrow column and a 18 pt gutter, it is easy to figure that the remaining text column is 29p6. This sort of grid is relatively easy to set up, and if any changes are made, they will be easy to implement.

The same thing applies with type measures. Ten-on-twelve-point type is easier to work with than 0.1389 inch on 0.1667 inch or 3.528 mm on 4.233 mm type. You can easily see that 14 lines of 12 pt leading are 14 picas deep. It is not so easy to figure 14 times 0.1667. The same thing applies to all type parameters. The font is sized in points, so the job is easier to work with if the leading, indents and spacing, tabs and so on are in the same units.


I once worked on an annual report that was specced as A4, which is a European size, 210 mm by 297 mm. In imperial units, this is a very awkward 8.2677 inches by 11.6929 inches. Since paper sheets here are sized so that signatures can be cut down to imperial sizes, very commonly 8-1/2 by 11 inches, this design decision required that larger paper be purchased and cut down, increasing waste and cost, just to produce a booklet in an unusual size. Then, as the job neared completion, the designer insisted that it was the wrong size. It turned out that she believed that A4 was an imperial size 8-1/4 inches by 11-1/2 inches, not a metric size at all. This required considerable extra expense to change. Unless you are ordering European-sized paper and your printer is set up to print and trim to metric specifications, millimetres have no place in design and are just going introduce the possibility of expensive problems.

The point

The point of all this is that while paper is made and handled in imperial sizes, in design, it should be specced in simple inch measures. Type and typography, including specifications for such things as margins and gutters, as well as type-style specifications, should be handled in points and picas. And in all cases, where possible, measures should be in whole numbers and simple whole-number fractions like 1/2, 3/4 or 7/8 for inches or 36pt, 4p6 or 5p3 for the corresponding pica measures. Don’t be the person who creates documents with arbitrary, awkward dimensions that are difficult to work with and that drive people like me mmm-mmmm-mmm-m mad.

CAPIC: Double Vision

Double Vision: the faces of CAPIC, the Toronto Chapter’s premier show and Yuletide celebration, will be celebrating its fifth year at Toronto Image Works on Friday, December 11th, 2009, with a festive spread and the room chock-full of attendees, who will choose the winning pairs of portraits by popular vote.

Dave needs a posse Dec 11 19:00:00. Anyone feelin artsy-fartsy? It is the CAPIC Double Vision show. It will be won by whoever has the biggest posse. The art is irrelavant.

Portrait: John Narvali by Dave McKay
Portrait: John Narvali by Dave McKay


I really love working on materials aimed at kindergarten to grade nine students. These are the years of wonder when all the coolest things you will ever learn about are new to you. Dinosaurs, planets, weather and volcanoes are insuperable discoveries inspiring awe that you are unlikely to feel later when learning about the third-person singular present subjunctive or tax reductions on depreciable property. What can ever measure up to the discovery that there were tyrannosaurs?

Working on school materials gives me a feeling like I had long years ago when “How Clouds Work” was a world-expanding idea to me.

The Solar System

Solar System Grade Nine
Solar System Grade Nine
Solar System Grade Seven
Solar System Grade Seven

These two solar systems were drawn for the same client, Nelson Canada, for two different grade levels. The top figure is for a grade nine text. The bottom figure is for a grade seven text. As you can see the amount of information and the complexity is increased greatly over two grade levels. In particular the grade 9 illustration shows the orbits of the bodies with far greater accuracy.

How to show the planet’s orbits when rendering the solar system is always a problem. If the entire disc of the solar system is shown in proportion (below right), then not only do all the bodies, including the sun, appear as tiny dots, the entire set of inner-planet orbits appears too small to show any detail. The diagram below on the left shows the inner-planet orbits in relation to that of Jupiter. Below and on the right, the orbits of all the planets are shown with the inner planet orbits tiny in proportion.

Inner and Outer Planetary Orbits Showing Proportions
Inner and Outer Planetary Orbits Showing Proportions

Therefore all solar system diagrams involve a compromise between accuracy and readability that can be determined by looking at the content the figure is intended to illustrate.