...

"Size" is the number of bytes on the wire, and "content" is the actual size of the resource. A number of things can make them different, including:

* Being served from cache (small or 0 "size")

* GZip encoding (smaller size than content)

* Request/Response headers, including cookies (larger size than content)

* Redirects or authentication requests

...

So I was a little surprised when I was checking the network tab on a typical street view page on Google maps and observed that the size of almost every tile (JPEG) was 0 but it wasn't being served from a local cache nor was it gzipped.

Here's what I see (note 6th column, Size/Content): http://i.imgur.com/VpENUSC.png

How is this happening, how can the file they transfer be 0 on the wire but definitely have content (as indicated) without caching or gzipping?

I'd love some more clarification if I'm misunderstanding something obvious. Thanks!