Hi, I've stumbled upon old thread on "locator and cached_location_t" [1] There are some interesting explanations which I believe is worth to add to Boost.GIL docs. Particularly, I believe the following Lubomir's clarification should be added as first paragraph documenting cached location: "Cached location is meant to be used as a quick way to get to neighborhood pixels if you need to read or write a neighboring location frequently relative to a given locator." Currently, notion of cached location is documented in the GIL design guide [1] but it makes users to deduce answer to "What the cached locator is for?". BTW, I wanted to provide patch, but I'm not sure where this update should be put or if I should submit a ticket. [1] http://lists.boost.org/Archives/boost/2010/12/174157.php [2] http://www.boost.org/doc/libs/1_51_0/libs/gil/doc/html/gildesignguide.html Best regards, -- Mateusz Loskot, http://mateusz.loskot.net