Are you sure the unit of measurement used is that important?
Joe Clark, in his book Building Accessible Websites, argues that web designers should not get overly concerned with the issue of whether text is resizable on the pages they design.
His argument stems from his definition of 'visually-impaired people', as only those who need to use assistive technology on their computers to access the web. Having defined visually impaired people thus, he considers that the units a designer uses to set text on a web page 'are essentially irrelevant to the actual visually-impaired people' [because] ' Accessibility is handled exclusively by the visitor's adaptive technology'. (p 223).
In other words, it doesn't matter what unit of measurement you use, because visually-impaired users will use whatever bit of technology they already have installed on their computer, to magnify, read out, or convert to braille, the text on the screen.
The only people, who will be affected by the choice of unit, therefore, will be 'normal-vision people who find the task of reading that specific page difficult.'(p223). And these people should not be our concern because they are not visually impaired people - and, therefore, outside the remit of accessible web design.
The argument has an attractive logic to it, however, I see some problems with this approach:
It assumes that accessible web design is only about making pages accessible to people with physical or cognitive impairments - and this is not a definition that I agree with. Although we want to design pages that will be flexible enough to be used by people with many different impairments - defining accessible web design only in those terms does not help us address the wider issues of site management, content re-use and making sure our pages will work on the widest range of web-enabled devices. I would group assistive technologies in with all the other bits of client technology used to access the web - and I want to have web pages that work on them all.
- In What is an accessible website?, I have discussed the implications for web designers and website managers, regarding defining accessible web design in particular ways - and suggest a definition that leads to the development of some practical guidelines.
- As someone with 'good' eyesight I come across many websites where I need to increase the size of the text to read the page comfortably. An approach that assumes that as a user if I want to make the text bigger I will be using screen magnfication software to do so seems unnecessarily restrictive.
It does not take into account the well worn argument, that it is the barrier to access that makes a person disabled, not their particular impairment. For example, I'm disabled by the fact that the text on the screen is too small for me to read and I can't change it, not by the fact that my eyesight is not as good as it once was. Remove the barrier, i.e. allow me to resize the text and, in this particular situation, I'm no longer disabled - even though my eyesight is the same as it was when I couldn't read the text.
- The issue that needs to be addressed here is whether or not it is easy for me to resize the text - and that is related to the choice of unit used to set text sizes on the page.
- If true, the points Joe Clark makes, undermine my argument that we should use relative rather than absolute units when setting text size in our pages; legitimating the use of, for example, points and pixels for setting text sizes on web pages. The case against using points is fairly straighforward and we will explore the arguments shortly. The case against using pixels is less clear cut, as pixels can be defined both as a relative or absolute units, depending on the capability of the device and web browser being used to view the page.
- I don't recommend using pixels to set the size of text on web pages, because for many users pixels effectively 'act like' an absolute unit - i.e. many users will not be able to resize the text easily.
Although, I disagree with Joe Clark's approach on this point, I largely support his general approach to accessible web design; and I would recommend Building Accessible Websites.
The other issue that we need to address - and one that can be killed off with less resistance - is that you should use absolute units of measurements to set the size of text on your page. This practice seems to stem from the misguided idea that it is the only way a designer can take complete control over how their webpages will look.