I recently considered getting either the Think Tank City walker 20 and Retrospective 7, thinking they were close in size - NOT.
The Citiwalker is at least 2 inches wider at the top. The bag is similar in size to the Retrospective 7, but I came out of the store with the City Walker 20. I liked the appearance and feel of the Retrospective, but didn't like the lack of a security closure latch. Velcro alone doesn't work for me.
While the Think Tank measurements are accurate, they don't tell the whole story. The City Walker is wider at the top than the bottom, and is a larger bag than the Retrospective 7. That works fine for me.
I recommend always examining a bag you want to purchase in advance of purchase. I was fortunate in having a real camera store within a reasonable drive. There aren't many left.
