Filter URLs - should I list name & value?

I’m in the process of incorporating a series of filters in my new site design and I was considering the SEO implications of different approaches.

I’ve seen some sites use key/value pairs in their friendly URLs eg /size/small/location/london
But I’ve also seen sites just use the value eg. /small/london

Given that there can be an indeterminate number of filters, I’m assuming that the second approach will only work if you ensure that values are unique. I’m also assuming that it’s important to enforce and ordering to the filters so that you don’t get /small/london as well as /london/small as this would represent duplicate content.

The second approach gives more concise and (arguably) readable URLs. And it seems to be richer in targeted keywords for searches like “small flats” (more likely than “flats size small”).
However is there a benefit in having a semantic relationship between name and value, such that Google would know that the ‘small’ keyword relates to size, or that the value ‘london’ does relate to the location, which might appear more relevant for searches like “flats in London”?