If you want a nicer plot, try scaling:
Plot3D[(1/(2*Pi))*(1/0.2)*(1/0.5)*(1/
6)*(Exp[-(0.5/0.04)*(x + 2.0)^2]*Exp[-(0.5/0.25)*(y - 1.2)^2] +
Exp[-(0.5/0.04)*(x + 0.5)^2]*Exp[-(0.5/0.25)*(y - 1.5)^2] +
Exp[-(0.5/0.04)*(x - 1.4)^2]*Exp[-(0.5/0.25)*(y - 2.9)^2] +
Exp[-(0.5/0.04)*(x - 3.1)^2]*Exp[-(0.5/0.25)*(y - 3.1)^2] +
Exp[-(0.5/0.04)*(x - 4.3)^2]*Exp[-(0.5/0.25)*(y - 3.3)^2] +
Exp[-(0.5/0.04)*(x - 5.7)^2]*
Exp[-(0.5/0.25)*(y - 4.2)^2]), {x, -4, 8}, {y, -4, 8},
PlotRange -> {0, 0.5}, ScalingFunctions -> {10^4 # &, #/10^4 &}]