As mentioned by others in the comments, you an use \path to update the current relative position.  ++(…) is relative to the last saved position within a particular path, but the start of a path is relative to (0,0). Consider the following example:

\documentclass{article}
\usepackage{tikz}
\begin{document}
\begin{tikzpicture}
\node at (0,0) {O};% label the origin
\node at ++(1, 0) [orange] {A};% this is relative to (0,0)
\node at ++(2, 0) [green] {B};% still relative to (0,0)
\path ++(2, 0) ++ (1,0) node [blue] {C};% start relative to (0,0), go to (2,0) and then relative to this end up at (3,0)
\path ++(5,0) ++ (1,0) node [red] {D};
\end{tikzpicture}
\end{document}




The lines starting with \node at ++(1, 0) and \node at ++(2, 0), are both relative to (0,0).  The subsequent lines starting with \path ++(2, 0) ... starts the path relative to (0,0), and moves to (2,0), and the subsequent ++ (1,0) is relative to the last point and hence the C is placed at (3,0). Note that that nothing was placed at (2,0) during this path.

Just to be sure, the last \path sets the current coordinate to (5,0) and nothing is added to the picture there, only at (6,0) do we see D.

How can you update the current relative coordinate in TikZ without adding an element?
Which is the best introductory textbook for Bayesian statistics?

One book per answer, please.
