I don't think anything should influence the bounding box, but still I get a lot of white space above my tikzpicture. No idea how to fix it. Also not sure how to post picture here (other than link).
\documentclass[12pt,a4paper]{amsart}
\usepackage{amsfonts}
\usepackage{amsthm}
\usepackage{amstext}
\usepackage{amsmath}
\usepackage{amscd}
\usepackage{amssymb}
\usepackage[mathscr]{eucal}
\usepackage{epsf}
\usepackage[margin=3cm]{geometry}
\usepackage{enumerate}
\usepackage{tikz}
\usepackage{url}
\usepackage[shortlabels]{enumitem}
\begin{document}
\begin{center}
\tikzset{every picture/.style={line width=0.75pt}} %set default line width to 0.75pt
\begin{tikzpicture}[x=0.75pt,y=0.75pt,yscale=-1,xscale=1]
%uncomment if require: \path (0,347); %set diagram left start at 0, and has height of 347
%Shape: Square [id:dp3326266826077382]
\draw (20,20) -- (300,20) -- (300,300) -- (20,300) -- cycle ;
%Shape: Rectangle [id:dp6598308172915477]
\draw [color={rgb, 255:red, 245; green, 166; blue, 35 } ,draw opacity=1 ] (20,160) -- (76,160) -- (76,300) -- (20,300) -- cycle ;
%Shape: Rectangle [id:dp9607631960830196]
\draw [color={rgb, 255:red, 245; green, 166; blue, 35 } ,draw opacity=1 ] (132,20) -- (188,20) -- (188,300) -- (132,300) -- cycle ;
%Shape: Rectangle [id:dp4913602627234861]
\draw [color={rgb, 255:red, 245; green, 166; blue, 35 } ,draw opacity=1 ] (244,20) -- (300,20) -- (300,160) -- (244,160) -- cycle ;
%Shape: Square [id:dp18637311726481443]
\draw (340,20) -- (620,20) -- (620,300) -- (340,300) -- cycle ;
%Shape: Rectangle [id:dp10879462581888877]
\draw [color={rgb, 255:red, 245; green, 166; blue, 35 } ,draw opacity=1 ] (340,160) -- (396,160) -- (396,300) -- (340,300) -- cycle ;
%Shape: Rectangle [id:dp042590528044432974]
\draw [color={rgb, 255:red, 245; green, 166; blue, 35 } ,draw opacity=1 ] (452,20) -- (508,20) -- (508,300) -- (452,300) -- cycle ;
%Shape: Rectangle [id:dp8368133041216019]
\draw [color={rgb, 255:red, 245; green, 166; blue, 35 } ,draw opacity=1 ] (564,20) -- (620,20) -- (620,160) -- (564,160) -- cycle ;
%Shape: Square [id:dp6432556650031391]
\draw [color={rgb, 255:red, 144; green, 19; blue, 254 } ,draw opacity=1 ] (340,230) -- (348,230) -- (348,300) -- (340,300) -- cycle ;
%Shape: Square [id:dp8501351470086091]
\draw [color={rgb, 255:red, 144; green, 19; blue, 254 } ,draw opacity=1 ] (356,160) -- (364,160) -- (364,300) -- (356,300) -- cycle ;
%Shape: Square [id:dp024380291880052418]
\draw [color={rgb, 255:red, 144; green, 19; blue, 254 } ,draw opacity=1 ] (372,160) -- (380,160) -- (380,230) -- (372,230) -- cycle ;
%Shape: Square [id:dp8865615238851052]
\draw [color={rgb, 255:red, 144; green, 19; blue, 254 } ,draw opacity=1 ] (388,160) -- (396,160) -- (396,230) -- (388,230) -- cycle ;
%Shape: Square [id:dp0614665698795509]
\draw [color={rgb, 255:red, 144; green, 19; blue, 254 } ,draw opacity=1 ] (596,20) -- (604,20) -- (604,90) -- (596,90) -- cycle ;
%Shape: Square [id:dp11443805463112966]
\draw [color={rgb, 255:red, 144; green, 19; blue, 254 } ,draw opacity=1 ] (580,20) -- (588,20) -- (588,160) -- (580,160) -- cycle ;
%Shape: Square [id:dp750623688120593]
\draw [color={rgb, 255:red, 144; green, 19; blue, 254 } ,draw opacity=1 ] (564,90) -- (572,90) -- (572,160) -- (564,160) -- cycle ;
%Shape: Square [id:dp3613640006001597]
\draw [color={rgb, 255:red, 144; green, 19; blue, 254 } ,draw opacity=1 ] (452,160) -- (460,160) -- (460,300) -- (452,300) -- cycle ;
%Shape: Square [id:dp071060074357018]
\draw [color={rgb, 255:red, 144; green, 19; blue, 254 } ,draw opacity=1 ] (468,20) -- (476,20) -- (476,300) -- (468,300) -- cycle ;
%Shape: Square [id:dp8403148942291725]
\draw [color={rgb, 255:red, 144; green, 19; blue, 254 } ,draw opacity=1 ] (484,20) -- (492,20) -- (492,160) -- (484,160) -- cycle ;
%Shape: Square [id:dp4948036396612854]
\draw [color={rgb, 255:red, 144; green, 19; blue, 254 } ,draw opacity=1 ] (500,20) -- (508,20) -- (508,160) -- (500,160) -- cycle ;
%Shape: Square [id:dp7751051729261558]
\draw [color={rgb, 255:red, 144; green, 19; blue, 254 } ,draw opacity=1 ] (612,20) -- (620,20) -- (620,90) -- (612,90) -- cycle ;
%Curve Lines [id:da04472292148459256]
\draw (48,300.34) .. controls (81.33,332.02) and (119.23,330.04) .. (158.8,300.89) ;
\draw [shift={(160,300)}, rotate = 143.13] [color={rgb, 255:red, 0; green, 0; blue, 0 } ][line width=0.75] (10.93,-3.29) .. controls (6.95,-1.4) and (3.31,-0.3) .. (0,0) .. controls (3.31,0.3) and (6.95,1.4) .. (10.93,3.29) ;
%Curve Lines [id:da7471540339883456]
\draw (160,300) .. controls (193.5,331.84) and (259.67,276.9) .. (271.82,161.74) ;
\draw [shift={(272,160)}, rotate = 95.73] [color={rgb, 255:red, 0; green, 0; blue, 0 } ][line width=0.75] (10.93,-3.29) .. controls (6.95,-1.4) and (3.31,-0.3) .. (0,0) .. controls (3.31,0.3) and (6.95,1.4) .. (10.93,3.29) ;
%Curve Lines [id:da04183912988012217]
\draw (344,300) .. controls (377.33,331.68) and (415.23,330.04) .. (454.8,300.89) ;
\draw [shift={(456,300)}, rotate = 143.13] [color={rgb, 255:red, 0; green, 0; blue, 0 } ][line width=0.75] (10.93,-3.29) .. controls (6.95,-1.4) and (3.31,-0.3) .. (0,0) .. controls (3.31,0.3) and (6.95,1.4) .. (10.93,3.29) ;
%Curve Lines [id:da5730355962662446]
\draw (456,300) .. controls (489.5,331.84) and (551.05,245.22) .. (567.75,161.27) ;
\draw [shift={(568,160)}, rotate = 100.96] [color={rgb, 255:red, 0; green, 0; blue, 0 } ][line width=0.75] (10.93,-3.29) .. controls (6.95,-1.4) and (3.31,-0.3) .. (0,0) .. controls (3.31,0.3) and (6.95,1.4) .. (10.93,3.29) ;
%Curve Lines [id:da9917744080887023]
\draw (568,90) .. controls (510.33,-67.66) and (383,21.68) .. (360,160) ;
\draw [shift={(360,160)}, rotate = 279.44] [color={rgb, 255:red, 0; green, 0; blue, 0 } ][line width=0.75] (10.93,-3.29) .. controls (6.95,-1.4) and (3.31,-0.3) .. (0,0) .. controls (3.31,0.3) and (6.95,1.4) .. (10.93,3.29) ;
%Curve Lines [id:da7864020859986232]
\draw [color={rgb, 255:red, 208; green, 2; blue, 27 } ,draw opacity=1 ] (360,300) .. controls (393.33,331.68) and (431.23,329.7) .. (470.8,300.55) ;
\draw [shift={(472,299.66)}, rotate = 143.13] [color={rgb, 255:red, 208; green, 2; blue, 27 } ,draw opacity=1 ][line width=0.75] (10.93,-3.29) .. controls (6.95,-1.4) and (3.31,-0.3) .. (0,0) .. controls (3.31,0.3) and (6.95,1.4) .. (10.93,3.29) ;
%Curve Lines [id:da42830860026959616]
\draw [color={rgb, 255:red, 208; green, 2; blue, 27 } ,draw opacity=1 ] (472,300) .. controls (505.5,331.84) and (567.71,259.08) .. (583.76,161.47) ;
\draw [shift={(584,160)}, rotate = 99.05] [color={rgb, 255:red, 208; green, 2; blue, 27 } ,draw opacity=1 ][line width=0.75] (10.93,-3.29) .. controls (6.95,-1.4) and (3.31,-0.3) .. (0,0) .. controls (3.31,0.3) and (6.95,1.4) .. (10.93,3.29) ;
%Curve Lines [id:da7536411477198044]
\draw [color={rgb, 255:red, 208; green, 2; blue, 27 } ,draw opacity=1 ] (584,20) .. controls (478.33,-16.32) and (399,21.68) .. (376,160) ;
\draw [shift={(376,160)}, rotate = 279.44] [color={rgb, 255:red, 208; green, 2; blue, 27 } ,draw opacity=1 ][line width=0.75] (10.93,-3.29) .. controls (6.95,-1.4) and (3.31,-0.3) .. (0,0) .. controls (3.31,0.3) and (6.95,1.4) .. (10.93,3.29) ;
%Curve Lines [id:da9293457318034677]
\draw [color={rgb, 255:red, 126; green, 211; blue, 33 } ,draw opacity=1 ] (376,230) .. controls (478.33,358.34) and (487,363.01) .. (488,160) ;
\draw [shift={(488,160)}, rotate = 90.28] [color={rgb, 255:red, 126; green, 211; blue, 33 } ,draw opacity=1 ][line width=0.75] (10.93,-3.29) .. controls (6.95,-1.4) and (3.31,-0.3) .. (0,0) .. controls (3.31,0.3) and (6.95,1.4) .. (10.93,3.29) ;
%Curve Lines [id:da31395724084484544]
\draw [color={rgb, 255:red, 126; green, 211; blue, 33 } ,draw opacity=1 ] (488,160) .. controls (599.77,205.45) and (595.05,176.64) .. (599.93,91.29) ;
\draw [shift={(600,90)}, rotate = 93.31] [color={rgb, 255:red, 126; green, 211; blue, 33 } ,draw opacity=1 ][line width=0.75] (10.93,-3.29) .. controls (6.95,-1.4) and (3.31,-0.3) .. (0,0) .. controls (3.31,0.3) and (6.95,1.4) .. (10.93,3.29) ;
%Curve Lines [id:da435351615237183]
\draw [color={rgb, 255:red, 126; green, 211; blue, 33 } ,draw opacity=1 ] (600,20) .. controls (494.33,-16.32) and (415,21.68) .. (392,160) ;
\draw [shift={(392,160)}, rotate = 279.44] [color={rgb, 255:red, 126; green, 211; blue, 33 } ,draw opacity=1 ][line width=0.75] (10.93,-3.29) .. controls (6.95,-1.4) and (3.31,-0.3) .. (0,0) .. controls (3.31,0.3) and (6.95,1.4) .. (10.93,3.29) ;
%Curve Lines [id:da46919834214932754]
\draw [color={rgb, 255:red, 155; green, 155; blue, 155 } ,draw opacity=1 ] (392,230) .. controls (494.33,358.34) and (503,363.01) .. (504,160) ;
\draw [shift={(504,160)}, rotate = 90.28] [color={rgb, 255:red, 155; green, 155; blue, 155 } ,draw opacity=1 ][line width=0.75] (10.93,-3.29) .. controls (6.95,-1.4) and (3.31,-0.3) .. (0,0) .. controls (3.31,0.3) and (6.95,1.4) .. (10.93,3.29) ;
%Curve Lines [id:da8428496850662717]
\draw [color={rgb, 255:red, 155; green, 155; blue, 155 } ,draw opacity=1 ] (504,160) .. controls (615.77,205.45) and (611.05,176.64) .. (615.93,91.29) ;
\draw [shift={(616,90)}, rotate = 93.31] [color={rgb, 255:red, 155; green, 155; blue, 155 } ,draw opacity=1 ][line width=0.75] (10.93,-3.29) .. controls (6.95,-1.4) and (3.31,-0.3) .. (0,0) .. controls (3.31,0.3) and (6.95,1.4) .. (10.93,3.29) ;
% Text Node
\draw (152,313.4) node [anchor=north west][inner sep=0.75pt] {$f_{1}$};
% Text Node
\draw (472,323.4) node [anchor=north west][inner sep=0.75pt] {$f_{2}$};
% Text Node
\draw (38.67,168.4) node [anchor=north west][inner sep=0.75pt] {$A_{0}$};
% Text Node
\draw (258.67,28.4) node [anchor=north west][inner sep=0.75pt] {$A_{2}$};
% Text Node
\draw (147.33,28.4) node [anchor=north west][inner sep=0.75pt] {$A_{1}$};
% Text Node
\draw (312.67,256.4) node [anchor=north west][inner sep=0.75pt] [font=\footnotesize] {$A_{00}$};
% Text Node
\draw (398,198.4) node [anchor=north west][inner sep=0.75pt] [font=\footnotesize] {$A_{03}$};
% Text Node
\draw (364,241.73) node [anchor=north west][inner sep=0.75pt] [font=\footnotesize] {$A_{02}$};
% Text Node
\draw (334.67,185.73) node [anchor=north west][inner sep=0.75pt] [font=\footnotesize] {$A_{01}$};
% Text Node
\draw (509.33,95.07) node [anchor=north west][inner sep=0.75pt] [font=\footnotesize] {$A_{13}$};
% Text Node
\draw (478,169.07) node [anchor=north west][inner sep=0.75pt] [font=\footnotesize] {$A_{12}$};
% Text Node
\draw (444.67,114.4) node [anchor=north west][inner sep=0.75pt] [font=\footnotesize] {$A_{11}$};
% Text Node
\draw (428,237.73) node [anchor=north west][inner sep=0.75pt] [font=\footnotesize] {$A_{10}$};
% Text Node
\draw (621.33,53.07) node [anchor=north west][inner sep=0.75pt] [font=\footnotesize] {$A_{23}$};
% Text Node
\draw (590,99.73) node [anchor=north west][inner sep=0.75pt] [font=\footnotesize] {$A_{22}$};
% Text Node
\draw (552,55.07) node [anchor=north west][inner sep=0.75pt] [font=\footnotesize] {$A_{21}$};
% Text Node
\draw (537.33,118.4) node [anchor=north west][inner sep=0.75pt] [font=\footnotesize] {$A_{20}$};
\node at (336,360,1) {\textit{Fig. 6}};
\end{tikzpicture}
\end{center}
\end{document}
\useasboundingbox (0,0) rectangle (5,5);- with suitable coordinates – hpekristiansen Jan 31 '22 at 21:35