2D - What Does it Mean?
I thought I would devote this page to a quick physics lesson on dimensions, since a lot of people know what 3D is, or at least have an idea, but seem to forget about 1D and 2D.
1-dimensional items can be most easily related to a line. Picture an x-y axis. The x-axis which is a line, is one dimensional. Anything that stays within just the x-axis, only has one dimension. If you were to draw one line in any direction on a sheet of paper, that would be a 1 dimensional line.
2 dimensional object consist of more than one line that exist on a plane. They have measurable dimensions when placed on an x-y axis. It must have no thickness to it. If you were to draw a rectangle, a circle, a triangle, or any other shape on a sheet of paper, this would be two dimensional.
If you've ever taken any type of physics class, you learned that everything your math teacher taught you about there being only and x-y axis is wrong. There is also a z-axis. If you were to draw an x-y axis with the x running horizontally, the y running vertically perpendicular to the x-axis, the z-axis when represented on paper runs through the middle of the intersection of the x-y axis. When drawn on paper, this is a 2D representation of the three dimensions. For example, when you draw a cube on a sheet of paper, this is still 2D, but it is a 3D representation, unlike a drawing of a square. 3D movies are labeled as 3 dimensional, but they are really just a 3D representation of a 2D object. Next time you go to see a 3D movie, take your 3D glasses off, and you can see that the picture on the screen is still 2D, but the shapes are distorted so that when you have the glasses on, you perceive the movie as being in 3D.
For more information on coordinates and dimensionality check out this Math is Fun link.
So how does this relate to barcodes? UPC barcodes are one dimensional since they contain information in one direction, horizontally. A 2D QR code can be read horizontally and vertically making it two dimensional.