medium might be greater along a horizontal plan than along a vertical one. Heterogeneous media have non-uniform properties of anisotropy or isotropy, while homogeneous media are uniform in their characteristics Local flow system Relief Direction of fl Local flow system Intermediate flow system Figure 1. 4 Definition sketches of groundwater systems(from Toth, 1963) 7medium might be greater along a horizontal plan than along a vertical one. Heterogeneous media have non-uniform properties of anisotropy or isotropy, while homogeneous media are uniform in their characteristics. Figure 1.4 Definition sketches of groundwater systems (from Toth, 1963) 7