With the exception of the indicator for slum improvements, most indicators proposed here are already collected by UN agencies, national governments, or broadly by cities. Data on PM10/2.5 air pollution concentrations are available for over 1 100 cities globally, and are maintained by the WHO Global Observatory. Data on slums are available for more than 60 countries (UN Habitat). Data on homicides are available through the WHO database on mortality by cause as well as from the UN Office on Drugs and Crime.27 WHO also maintains data from multi-country studies on domestic violence and women's health, which can be disaggregated for cities
For urban transport, data on the percent of pedestrian/cycle mortality as a proportion of total traffic mortality is available for 135 countries.28 In some highly motorized countries, this proportion may not adequately reflect the "pedestrian-cycle" quality of the urban environment, but rather the sheer lack of travel by non-motorized transit (NMT) modes. For this reason, a more sensitive indicator would be the proportion of pedestrian/cycle deaths by kilometres of pedestrian/cycle travel – which is relatively easy to deduce once travel by NMT modes is routinely monitored and reported. Health sector support for the expanded use of this indicator would reinforce efforts by countries, cities, and civil society to focus on this all-important linkage between urban environment, health and safety.