Z-order of points in scatterplot

Question

I have the following scatter plot done with pgfplots:

The meta value of each point represents its "importance", hence red points are more important of blue ones. The problem is that red and orange points are buried among all the blue points, especially around (0,0). Is it possible to draw points with a z-order proportional to their meta value, i.e., having red and orange points in front of the blue ones?

Here's my code:

\documentclass{article}

\usepackage{tikz}
\usepackage{pgfplots}
\pgfplotsset{compat=newest}

\begin{document}

\pgfplotsset{
ytick={0,0.2,...,1},
xtick={0,0.2,...,1},
xmajorgrids=true,
ymajorgrids=true,
major grid style={dashed},
}

\begin{tikzpicture}
    \begin{axis}[xmin=0,xmax=1,ymin=0,ymax=1,colorbar horizontal]
        \addplot[scatter,
                 only marks,
                 mark size=1pt,
                 point meta=explicit,
                 point meta min={0},
                 point meta max={100}] table [col sep=comma, 
                                              x index=0, 
                                              y index=1, 
                                              meta index=2] {csv/scatter.csv};
    \end{axis}
\end{tikzpicture}

\end{document}

An example scatter.csv:

0.000000,0.000000,53
0.000000,0.000213,1
0.000000,0.007653,1
0.000000,0.017226,1
0.000000,0.030485,1
0.000000,0.032558,1
0.000000,0.034453,1
0.000000,0.039656,1
0.000000,0.050874,1
0.000000,0.061787,1
0.000000,0.065450,1
0.000000,0.151315,1
0.000000,0.184418,1
0.000000,0.201284,1
0.000000,0.217143,1
0.000000,0.250000,4
0.000000,0.255159,1
0.000000,0.257401,1
0.000000,0.268999,1
0.000000,0.331126,1
0.000000,0.333333,3

Answer 1

As Pouya suggested you can order the data. He proposed datatool but I'll use \pgfplotstablesort command from \pgfplotstable package.

I've changed some of your data to make more evident how the code works:

\documentclass{article}
\usepackage{pgfplotstable} 
\usepackage{pgfplots}   

\begin{document}
\pgfplotstableread[col sep=comma]{
X,Y, C
0.000000,0.000000,53
0.000000,0.000213,1
0.000000,0.007653,1
0.000000,0.017226,1
0.000000,0.030485,1
0.000000,0.032558,60
0.000000,0.034453,1
0.000000,0.039656,1
0.000000,0.050874,1
0.000000,0.061787,45
0.000000,0.065450,1
0.000000,0.151315,32
0.000000,0.184418,1
0.000000,0.201284,1
0.000000,0.217143,1
0.000000,0.250000,4
0.000000,0.255159,1
0.000000,0.257401,1
0.000000,0.268999,80
0.000000,0.331126,1
0.000000,0.333333,3
}\data

%get the data and sort by column 'C'
\pgfplotstablesort[sort key={C}]{\sorted}{\data} 

%Comment out next command to type the ordered table
%\pgfplotstabletypeset{\sorted}

\pgfplotsset{
ytick={0,0.2,...,1},
xtick={0,0.2,...,1},
xmajorgrids=true,
ymajorgrids=true,
major grid style={dashed},
}

\begin{tikzpicture}
    \begin{axis}[xmin=0,xmax=1,ymin=0,ymax=1,colorbar horizontal]
        \addplot[scatter,
                 only marks,
                 mark size=1pt,
                 point meta=explicit,
                 point meta min={0},
                 point meta max={100}] table [col sep=comma, 
                                              x index=0, 
                                              y index=1, 
                                              meta index=2] {\sorted};
    \end{axis}
\end{tikzpicture}
\end{document}

A little detail of the resulting figure looks like

Answer 2

You can (ab)use the builtin method of z buffer=sort: why not using the color data as third dimension combined with view={0}{90} (which means "view from top", i.e. from z = + infinity)?

The key z buffer=sort will sort keys such that those which are "far away" from the viewer (i.e. with small z value in our case) will be on the bottom and those which are "close" to the viewer (i.e. large z value in this picture) will be drawn on top of them.

Example:

\documentclass{standalone}

\usepackage{tikz}
\usepackage{pgfplots}
\pgfplotsset{compat=1.11}

\begin{document}

\pgfplotsset{
ytick={0,0.2,...,1},
xtick={0,0.2,...,1},
xmajorgrids=true,
ymajorgrids=true,
major grid style={dashed},
}

\begin{tikzpicture}
    \begin{axis}[xmin=0,xmax=1,ymin=0,ymax=1,colorbar horizontal,view={0}{90}]
        \addplot3[scatter,
                 only marks,
                 mark size=5pt,
                 z buffer=sort,
                 point meta=z,
                 point meta min={0},
                 point meta max={100}] 
         table[col sep=comma]
    {
0.000000,0.000000,53
0.000000,0.000213,1
0.000000,0.007653,1
0.000000,0.017226,1
0.000000,0.030485,1
0.000000,0.032558,1
0.000000,0.034453,1
0.000000,0.039656,1
0.000000,0.050874,1
0.000000,0.061787,1
0.000000,0.065450,1
0.000000,0.151315,1
0.000000,0.184418,1
0.000000,0.201284,1
0.000000,0.217143,1
0.000000,0.250000,4
0.000000,0.255159,1
0.000000,0.257401,1
0.000000,0.268999,1
0.000000,0.331126,1
0.000000,0.333333,3
0.5,0.5,100
0.51,0.51,0
0.49,0.51,50
    };
    \end{axis}
\end{tikzpicture}

\end{document}

I added three points in the middle and increased the mark size to verify that I sorted in the correct order. Turn off z buffer=sort to see that they are drawn in the order of appearance (i.e. wrong). The z buffer implicitly results in the correct ordering, and it has minimal overhead.