Tikz - grids there are not connected

Question

I have a problem regarding making a lots of grid i tikz.

my code is as follows:

 \begin{tikzpicture}
 \path[use as bounding box,draw] (12,18) rectangle (0,0);

 \foreach \x in {0,2,4,8}
 \draw[black] (0.999+\x,17) grid[step=0.2] (2+\x,15.999);

 \draw[->] (3.5,15.5) -- (3.5,13);
 \draw[->] (9.5,15.5) -- (9.5,13);

 \foreach \x in {2,4,6,8}
 \draw[black] (0.999+\x,12) grid[step=0.2] (2+\x,10.999);

  \draw[->] (6.5,10) -- (6.5,9);

  \draw[black] (5.999,8.100) grid[step=0.2] (7,7.099) node {};
  \end{tikzpicture}

One can clearly see that the grid in the third row are not drawn corretly.

Hope that any of your can help.

Answer 1

If you define your grid as small picture pic than you can rewrite your MWE as:

\documentclass[tikz, margin=3mm]{standalone}

\begin{document}
\begin{tikzpicture}[
   GRID/.pic={\draw (0,0) grid[step=0.2] (1,1);}
                    ]
\path[use as bounding box,draw] (12,18) rectangle (0,0);

\foreach \x in {1,3,5,9}
\pic at (\x,16) {GRID};
\draw[->] (3.5,15.5) -- (3.5,13);
\draw[->] (9.5,15.5) -- (9.5,13);
%\fill[red] (1,16) circle (1mm);% for test of pic coordinate

\foreach \x in {3,5,7,9}
\pic at (\x,11.5) {GRID};
\draw[->] (6.5,11) -- (6.5,9);

\pic at (6,7.5)  {GRID};
  \end{tikzpicture}
\end{document}

(image not contain bounding box).

Answer 2

Grids are shifted so that they always meet at the current origin. The trick is to shift the origin with the shift key:

\documentclass[tikz,border=5]{standalone}
\begin{document}
\begin{tikzpicture}
\draw [red] (0,0) grid +(4,4);
\draw [green, dashed] (0.5,0.5) grid +(4,4);
\draw [blue, dotted, shift={(0.5,0.5)}] (0,0) grid +(4,4);
\end{tikzpicture}
\end{document}