Critical infrastructures such as energy, transport, water, waste and telecommunications exist as geospatial interdependent networks, supplying goods and services that support society and economy. The resilience of infrastructure networks is tested in external shocks, resulting in the potential for widespread cascading failures with catastrophic socio-economic consequences. For efficient resilience planning, there is a need to understand systemic vulnerabilities to prioritize resource allocation for network enhancement. We present a system-of-systems methodology to meet this need, by analysing the systemic resilience in terms of individual asset level and aggregated spatial vulnerability characteristics of interdependent critical infrastructure networks. We characterise the geospatial resilience of networks in terms of: (1) direct and indirect customers disruption potential; and (2) geographic spread of network failure cascades. Case-studies from UK (England and Wales only) and New Zealand demonstrate how these resilience metrics can rank systemic vulnerabilities, which are most critical to maintaining national functionality. Such a ranking provides the basis for prioritizing investment decisions for enhancing the resilience of large scale networks. National scale maps and visualisations are presented to communicate prioritised resilience building measures to stakeholders and decision makers, highlighting wider network vulnerabilities which might not otherwise be identified.