Abstract— This work provides a framework for the observability analysis of linear networked dynamic systems (NDS). A distinction is made between NDS that have homogeneous agent dynamics and NDS that have heterogeneous dynamics. In each case, conditions for the observability of such a system are presented; we will also quantify the relative degree of observability of these systems. Moreover, an index of homogeneity and an index of heterogeneity are introduced as the means of quantitatively measuring how homogeneous a particular NDS is.