What is the term for, and a list of, “continuous dialects”?

Question

I remember reading that Portuguese and Spanish are really just extremes on a continuum of a dialects. That is, if one travels slowly from (for example) Madrid to Lisbon, one would note nothing more than subtle shifts in dialect the entire way, and there is nothing significant about the shift around the area of the border. It's just that once you would reach Lisbon, the shifts have added up to a big difference from Madrid.

Firstly, is this true? Secondly, if so, what is the technical term for such a situation? And finally, is there a list of other language pairs that have this property?

Answer 1

This phenomenon is called language continuum or dialect continuum. According to Wikipedia:

In sociolinguistics, a language continuum is said to exist when two or more different languages or dialects merge one into the other(s) without a definable boundary. This happens, for example, across large parts of India. Historically, it also happened in various parts of Europe, for example in a line stretching from Portuguese to Walloon (in Belgium); from Portuguese to the southern Italian dialects; and between German and Dutch. Within the last 100 years or so, however, the increasing dominance of nation-states and their standard languages has been steadily eliminating the non-standard dialects of which these language continua were formed, making the boundaries ever more abrupt and well-defined.

That WP article cites several examples, from different language families, around the world.

Answer 2

You're so close. The term for this is

dialect continuum.

In the modern, industrialized, media-blanketed world, with centralized languages at the expense of marginal dialects, there are fewer true instances of dialect continua. The classic example is the German dialects from Bavarian in the far southeast through Frankish and Plattdeutsch to Dutch, where each community can understand the the neighboring community just fine, with no strict boundaries where there is mutual unintelligibility, but at the two extremes (or even halfway) one cannot understand the other.

But this doesn't have to be linear. It has been said that within the continent of Australia, the intelligibility is a neighborhood graph with no two particular endpoints, neighbors understand neighbors on all sides.