I tried to understand how the transform is working in D3 but I think I didn't get it.
Does the scale change the size of the SVG object ? meaning if I give a big number the size of the object will look bigger ? Does the translate move the object from one place to different place ? I tried it but it didn't work like I thought.
Could you please explain to me how it should work ?
The transforms are SVG transforms (for details, have a look at the standard; here are some examples). Basically, scale and translate apply the respective transformations to the coordinate system, which should work as expected in most cases. You can apply more than one transform however (e.g. first scale and then translate) and then the result might not be what you expect.
When working with the transforms, keep in mind that they transform the coordinate system. In principle, what you say is true -- if you apply a scale > 1 to an object, it will look bigger and a translate will move it to a different position relative to the other objects.
Scott Murray wrote a great explanation of this[1]. For instance, for the code snippet:
svg.append("g")
.attr("class", "axis")
.attr("transform", "translate(0," + h + ")")
.call(xAxis);
He explains using the following:
Note that we use attr() to apply transform as an attribute of g. SVG transforms are quite powerful, and can accept several different kinds of transform definitions, including scales and rotations. But we are keeping it simple here with only a translation transform, which simply pushes the whole g group over and down by some amount.
Translation transforms are specified with the easy syntax of translate(x,y), where x and y are, obviously, the number of horizontal and vertical pixels by which to translate the element.
[1]: From Chapter 8, "Cleaning it up" of Interactive Data Visualization for the Web, which used to be freely available and is now behind a paywall.
I realize this question is fairly old, but wanted to share a quick demo of group transforms, paths/shapes, and relative positioning, for anyone else who found their way here looking for more info:
Source: Stackoverflow.com