From b2a0a7f65c2a8cd2d16ee63f28d5ed1c19c69149 Mon Sep 17 00:00:00 2001 From: springmeyer Date: Mon, 27 Aug 2012 08:57:26 -0700 Subject: [PATCH] Created Expression (markdown) --- Expression.md | 5 +++++ 1 file changed, 5 insertions(+) create mode 100644 Expression.md diff --git a/Expression.md b/Expression.md new file mode 100644 index 0000000..aaf0031 --- /dev/null +++ b/Expression.md @@ -0,0 +1,5 @@ +Mapnik Expressions enable data-driven behavior in Mapnik. They are constructed from strings, can hold any kind of type of data, and are evaluated at render time. They are used by symbolizers like the [[TextSymbolizer]] to dynamically construct text labels for display and they are also the basis for how Mapnik [Filters](Filter) work. + +Recently, in Mapnik 2.1, expressions became enabled in the `transform` parser used to apply affine transformations to image and svg symbols. So, now you can not only, for example, rotate symbols with a transform like `transform="rotate(45)"` but the rotation can be data driven like `transform="rotate([field])"` + +For more info on the original design see: http://mapnik.org/news/2009/12/08/future_mapnik2/