Urban utilities, spatial data and interdependent infrastructure

Ask what depends on what

Water delivery can depend on electricity and communications; electricity restoration may depend on transport access and other services. A dependency statement should identify the function, direction and conditions. Sharing a corridor is a different relationship and may expose several systems to one physical disturbance.

A community resilience assessment connects assets to the services and activities they support. Restoring an individual component is not necessarily the same as restoring a usable service. A functioning pump cannot deliver through an unavailable downstream network, and an open road may still lack the connections needed for an essential journey.

A coordinate needs its reference

Spatial records need a coordinate reference system, units and an appropriate vertical reference where elevation matters. Similar-looking numbers can represent different positions under different definitions. A map display can reproject layers, but that does not certify the original survey, conversion or asset record.

The USGS lidar data dictionary illustrates the information carried alongside spatial data: acquisition dates, horizontal and vertical reference systems, projection and provenance. These fields tell a user what a record means. They are not a claim that every city dataset uses those systems or has the same accuracy.

Retain uncertainty and date as well as position. A centreline sketch, a surveyed asset and an inferred location are different evidence. Linking records by a nearby map symbol can be wrong, especially when services overlap vertically or records describe different historical states.

Test the dependency scenario

Backup capacity must be related to its service load and duration. An energy inventory and a power capability are separate constraints. Other dependencies, transfer behaviour and equipment condition may prevent the stored energy from producing the intended service.

The figure deliberately isolates energy and time. It assumes the backup is already qualified, transfers perfectly and faces no other limit. Real assessment would also examine common causes, restoration variation, alternative service paths and the consequence of interruption. Record which of those have actually been evaluated.

Balance a supplied backup energy inventory

Imagine a three-hour grid outage affecting a pump. Supply 6 kWh of fully usable backup energy and a constant 3 kW pump load. Assume perfect transfer, adequate power capability, no other losses, no other dependencies and no water storage that can replace pump service.

Runtime is 6 kWh /3 kW=2 h. Under these assumptions the pump has two hours of backup service followed by one hour without service. Doubling the outage does not double the backup inventory; it increases the uncovered interval to four hours.

If the same fully usable energy serves a 4 kW load instead, runtime is 1.5 h. This is an original finite-energy balance, not a battery rating, installation instruction or prediction for a real network. The words “fully usable” and “no other limit” are necessary inputs to its conclusion.

Try the reasoning

1. Does spatial co-location prove a functional dependency?

   Show the answer and reasoning

   No. The function, direction and operating conditions of the dependency must be established.

2. What are the dimensions of energy divided by power?

   Show the answer and reasoning

   Time; for example kWh divided by kW gives hours.

3. Does a complete spatial reference prove location accuracy?

   Show the answer and reasoning

   No. It defines the coordinates’ meaning; observation quality, date and uncertainty still need evidence.

What to carry forward

Connect assets to service functions and retain the meaning of their records.