Along with the standard measures of economic output and population density, livability is increasingly cited as a key metric by which to rank cities. At first glance, livability may seem like a nebulous concept culled from arbitrary ratings; however, major publications and news outlets have made livability rankings into a science and regularly publish their findings and methodologies. Livability indices are compiled by aggregating data from aspects of quotidian city life and weighting the data based on its relative importance to quality of life or the overall happiness of residents.

Certain indices are tailored to more specific audiences and will incorporate lifestyle metrics alongside traditional quality-of-life indicators. Each index uses a proprietary weighting scheme and is likely to produce different rankings as a result. This does not necessarily detract from the validity of the findings, but rather is indicative of the fact that different audiences have different priorities. At the most general level, livability indices take into account the cost of living, commute time, safety and environmental quality; narrowly-focused rankings may add more detailed attributes to the equation to better serve a specific audience.

For example, New York Magazine’s Neighborhood Livability Calculator lets users pick their top priorities to determine their ideal neighborhood based on their personal criteria and produces a responsive customized ranking. This index uses traditional cost of living and commute time metrics alongside other factors such as diversity and creative atmosphere, which could be more important than the quality of neighborhood schools for, say, a young artist with no children.

A livability index designed specifically for young adults gets even more creative with which metrics it uses. The news site Vocativ released a list of The 35 Best U.S. Cities for People 35 and Under which gave special consideration to some of the things they think matter most to that cohort. The index takes into consideration traditional livability metrics such as cost of rent, transit, weather and crime as well as less-visited metrics such as the cost of a night out on the town and an ounce of cannabis. Despite the grins or eye rolls that this may produce in some readers, who’s to say that this is not a valid component of livability for the target audience?

On a larger scale, livability indices hold water when compared to outside empirical data. It’s not surprising that the rankings of Damascus on global livability indices have plummeted during the ongoing Syrian civil war; in fact, over the past five years, cities in regions with political instability, terrorism and civil unrest are slipping to lower and lower ratings, as should be expected.

Ultimately, there is no absolute best livability index that can provide a one-size-fits-all ranking; human priorities are myriad and varied. However, defining and knowing the audience for a targeted index makes it tremendously more valuable to its users. Livability indices will undoubtedly continue to receive an increasing amount of attention as the global population becomes increasingly urbanized and can afford to demand a higher quality-of-life; the salient question of livability rankings will be “livable by whose standards?”