By "blobs", I mean a two-dimensional area. You need at least one d10 and multiple d6s. Roll these all at once in a large, clear space. The area we rolled the dice in represents an abstract map, which we read exactly as we would read a map laid out flat on the table in front of us: west and east are on the left and right, respectively, and the side closest to us is south.
If two d10s are next to each other with no intervening d6s, such as 1 and 2 in the example pic, the blobs overlap. All five six-sided dice describe Blob 1, while the 3, 4 and 5 describe Blob 2; the 3 and optionally the 5 describe Blob 3, which is adjacent to Blobs 1 and 2, but doesn't overlap.
The pic to the left illustrates turning a straight west-to-east line into a zig-zag. If the west and east ends aren't just directions, but sharply defined (as when drawing a road between cities,) the position of the endpoints would need to be altered.
The exact dice rolled, of course, depends on your needs, and what other dice you might be rolling simultaneously. Three dice will be fine in many cases, four is probably the most you will need. I used 4d6 in the example, but most of the specific procedures I will cover in the next post in the series will use d4 or d8, since d10 and d6 will usually be spoken for.
Sometimes, you don't need to know the two-dimensional location of each point on a line, but just need to know the numbers rolled in a particular order. For example, if you set up a climate or elevation gradient as described in the Central Casting post, you can use 4d4 to turn a straight slope into a climate or elevation profile for the entire map. Each 4 rolled means the elevation or temperature rises higher than expected, while each 1 rolled means it drops lower than expected; a 2 or 3 means the default slope is used.