Typefaces are often described as “based on” other typefaces. E.g.:
I understand “based on” to mean that the designer(s) of the later typeface were aware of the preceding one and were trying to emulate some of its visual characteristics so that, to a human, the later one would be reminiscent of the earlier one, in one or more ways.
Therefore: given two typefaces and no other information, it is in principle impossible to mechanically determine whether one was “based on” the other.
Sometimes, a typeface is described as “metrically compatible” with another typeface. E.g.:
- Cousine is “metrically compatible” with Courier New;
- Liberation Sans is “metrically compatible” with Arial.
I understand “metrically compatible” to mean that substituting a typeface with a metrically compatible one will not alter the text flow of the document, i.e. line breaks and pagination, etc, will remain the same.
Therefore: given two typefaces and no other information, it is in principle possible to mechanically determine whether they are metrically compatible.
Is my understanding, as presented above, correct? If not, what have I misunderstood?
Please can you quote any authorities you know of that corroborate your answer?
Is my understanding, as presented above, correct?
If not, what have I misunderstood?
Nothing. Spot on.
What I will say is that a font “based on” another may also be “metrically compatible” or it may be vastly different from the original, there’s not a whole lot you can assume based solely on the knowledge that a typeface was based on another.
It may also be that “metrically compatible” typefaces don’t align as completely as you assume. Although it should if advertised as such, there are a lot of metrics involved in type design and a lot of other things that affect text flow. The font may have different kerning values for example. They may also just be very similar so you’d see little change in most circumstances (but aren’t guaranteed not to).