I would say this depends on what quantities or phenomena you intend to study with this distance to the center. Indeed, you can think of different definitions for the city center, which will all be meaningful in different situations.

First, you can think of the geographical center. which is the center of gravity of the city's spatial footprint. This definition makes sense when you are trying to compute distances to a given city on a large scale.

Then, the 'population center' as you suggested, which is the center of weight of the city's total population. You can also think of an 'activity center', which would be the center of weight of the city's total employment. And so on... for every quantity you can think of, you can compute the center of weight and get a perfectly reasonable definition of the city center. Ultimately, the most reasonable definition depends on the context of your study.

Also, as you know, large cities are polycentric in terms of activity density and population density. Therefore, if the context of your study is intra-urban, I would be cautious with computing distances to a single, average center.

I hope this helps.

Näyhä et al. have located city centers by the most populous 1x1 km grid cell.

See Näyhä et. al. (2013). Body mass index and overweight in relation to residence distance and population density: experience from the Northern Finland birth cohort 1966. BMC Public Health 13:938.

http://www.biomedcentral.com/1471-2458/13/938

Thank you! That's an interesting approach. However, looking at population density maps I've often seen very low density in the center of the city, as central business districts may have little housing, e.g. https://googledrive.com/host/0B8z0KNOJamejXzg1a2psQkctNFE/sapporo_a.png (Sapporo, Japan). Maybe the approach in the paper could be extended - by calculating a "center of weight" based on population density...? This would take into account not only the most populous grid cell, but all grid cells.

I would say this depends on what quantities or phenomena you intend to study with this distance to the center. Indeed, you can think of different definitions for the city center, which will all be meaningful in different situations.

First, you can think of the geographical center. which is the center of gravity of the city's spatial footprint. This definition makes sense when you are trying to compute distances to a given city on a large scale.

Then, the 'population center' as you suggested, which is the center of weight of the city's total population. You can also think of an 'activity center', which would be the center of weight of the city's total employment. And so on... for every quantity you can think of, you can compute the center of weight and get a perfectly reasonable definition of the city center. Ultimately, the most reasonable definition depends on the context of your study.

Also, as you know, large cities are polycentric in terms of activity density and population density. Therefore, if the context of your study is intra-urban, I would be cautious with computing distances to a single, average center.

I hope this helps.

When I worked for a very well known global mapping company if someone typed NYC or LA or whatever city you have to route them to a point and say "you have arrived". Most often if not always we used city hall so almost all digital map data in the US has city hall as the location of the city in digital repositories. I say most 99.9% because occasionally city hall had upped and moved to the suburban part of the city.

Thank you for your answers, everyone!

Stuart, do you know if this was based on a definition or guideline, or was this just common practice? I wonder if there is some kind of document one could cite...

it was written in our database specification manual but i think some geographic history may apply. The county courthouse has historical served as the land title repository.

It depends on the context. In India in certain studies, main bus or railway station is taken as the city centre and in others it was main market where people from the rural areas sell and purchase goods. Even in others it has been geometric centre of the city (centroid). However, city centre for the purpose of the road distances from the city is General Post Office.

Very interesting question!!!

There are indeed no official city centers. Relying OpenStreetMap data of a whole country, we are able to identify the center of the country, i.e., the block with the highest border number far from the country border (center = topological center).

Jiang B. and Liu X. (2012), Scaling of geographic space from the perspective of city and field blocks and using volunteered geographic information, International Journal of Geographical Information Science, 26(2), 215-229. Reprinted in Akerkar R. (2013, editor), Big Data Computing, Taylor & Francis: London, Preprint: http://arxiv.org/abs/1009.3635

A follow-up work published in Physica A: http://www.sciencedirect.com/science/article/pii/S0378437114008565

You may wonder where the center of a city is. Following the same thinking, we can conclude that the block with the highest border number far from the city border is the city center. Then where is the city border? City border or the border of natural cities is defined as the border of a set of small blocks (smaller than the average).

Thanks for your post! That's some really fascinating research and an interesting approach, I will read your papers and may come back with questions! ;)