How can I draw an axis with values on some points?

Question

I think the figure is very simple.

Nevertheless, I can't figure out how to do it. Any help?

Answer 1

A very basic approach just to show the concept.

\documentclass[11pt]{article}
\usepackage[T1]{fontenc}
\usepackage{tikz}

\begin{document}
  \begin{tikzpicture}
    \draw (0,0) -- (6,0);
    \foreach \x/\xtext in {0/a,1/b,3/c,6/d}{
      \draw (\x cm,-2pt) -- (\x cm,2pt) node[above] {\xtext};
    }
  \end{tikzpicture}
\end{document}

For details you should take a look into the »pgf/tikZ« user guide.

---

Answer 2

I prefer an answer instead of a long comment but I want to say that it's preferable to use the same method to work with dimensions

If you wrote \draw (0,0) -- (6,0); then the code would be :

 \documentclass{minimal}
 \usepackage{tikz}
 \begin{document}
  \begin{tikzpicture}
    \draw (0,0) -- (6,0);
    \foreach \x/\xtext in {0/a,1/b,3/c,6/d}{
      \draw (\x ,-.08) -- (\x,0.08) node[above] {\xtext};
    }
  \end{tikzpicture} 

A problem can appear if later you use scale = 2 or x= 2 cm, y = 2 cm or if you want to use big numbers.

Why is important :

 \documentclass{minimal}
 \usepackage{tikz}
 \begin{document}
 \begin{tikzpicture}
  \draw (0,0)--(600,0);
 \end{tikzpicture}
\end{document} 

gives an error Latex Error : ... Dimension too large.

 \documentclass{minimal}
 \usepackage{tikz}
 \begin{document}
 \begin{tikzpicture}[x=0.01 cm]
  \draw (0,0)--(600 cm,0);
\end{tikzpicture}
\end{document} 

gives the same error

but

 \documentclass{minimal}
 \usepackage{tikz}
 \begin{document}
 \begin{tikzpicture}[x=0.01 cm]
    \draw (0,0)--(600,0);
  \end{tikzpicture}
 \end{document} 
\end{document} 

is correct. a dim is limited by 16 384 pt near 5.75 m but TeX can work with big numbers, the next code compiles but you can't replace x=0.00001 cm by x=0.000001 cm

\documentclass{minimal}
\usepackage{tikz}
\begin{document}
\begin{tikzpicture}[x=0.00001 cm]
 \coordinate (x) at (600000,0);
  \draw (0,0)--(x);
\end{tikzpicture}
\end{document}