Como criar esta grade circular no tikz?

Question

Sou meio novato no tikz, pessoal! Preciso desenhar uma figura parecida com essa! Alguém pode me ajudar?

Answer 1

\documentclass[border=3mm]{standalone}
\usepackage{tikz}
\colorlet{layer}{gray!50}
\colorlet{layerhl}{black!80} % highlighted layer
\tikzset{neuron/.style={draw=#1,circle,minimum width=2pt,inner sep=0pt}}
\newcommand\layer[3]% \layer{name}{size}{label}
  {\foreach \i in {1,...,#2}
     \foreach \j in {1,...,#2}
       \node[neuron=layer] (#1-\i-\j) at (\i,\j) {};
   \node[anchor=south] at (0.5*#2+0.5,#2+1) {#3};
  }
\begin{document}
\begin{tikzpicture}[x=3pt,y=3pt]
  \layer{input}{28}{input neurons}
  \begin{scope}[shift={(34,2)}]
    \layer{first}{24}{first hidden layer}
  \end{scope}
  % Highlighted part
  \node[neuron=layerhl] at (first-2-24) {};
  \foreach \i in {2,...,6}
    \foreach \j in {24,...,28}
      {\node[neuron=layerhl] at (input-\i-\j) {};
       \draw[->,layerhl] (input-\i-\j) -- (first-2-24);
      }
\end{tikzpicture}
\end{document}