Major issue with HR resources is not only the number, but the quality of ICT / other relevant specialists. The cities have a challenge in finding talented people, and are competing on them against the industry. Yet, outsourcing does not help since even consulting companies struggle to provide highly skilled specialists for some tasks.

a numerical indicator could for example be number of professionals with certain level of a degree (Bachelors, Masters, higher)

Also: are their training being kept up to date? Any kind of degree in ICT is rapidly outdated. Frequency of update training is also a good indicator.

Also in this case the number can be misleading as it depends on the size of the local PA

I dont think the number of ICT specialists (they can have many different orientations) is an indicator, an enabler

Number can be misleading also since cities use outsourcing in ICT-services, number of specialist on the city payroll doesn't give the whole picture about the capabilities city has in use.

i would say as indicator: percentage of annual budget towards internal and external expertise booked on IT projects?