MapnikCoreConcepts.md

+# Core Concepts of Mapnik
+
+Mapnik can be used with XML, Python or C++, but the key concepts are the same across these technologies. For details on how to use the different APIs, see [[LearningMapnik]].
+
+Mapnik creates maps. The *map* object is therefore central to Mapnik's API. The map object provides methods for rendering a map to a graphical output format (usually PNG or PDF).
+
+Maps are (mainly) made up of arbitrary numbers of *layers*. Each layer has a *datasource* that provides the geometry data (provided by one of several *plugins* that read and parse the data). For rendering the data, each layer can be assigned one or multiple styles.
+
+A *style* defines how the objects in a layer are rendered. A style contains one or more *rules* that can optionally constrain its output to *filter* out a subset of the objects provided by the layers datasource, for example to show only these objects who have a specific attribute set. Filters are optional – a common case for simple maps is to have one rule for each layer without any filters. Each rule holds one or more *symbolizers* which are responsible for actually drawing geometry in the output. Depending on the symbolizer class and settings, geometry can be rendered in a variety of ways.
+
+The order of layers, rules and symbolizers is generally important in Mapnik, as the layering of output in the result image is not modelled explicitly (like, for example the `z-index` property in CSS), but determined by the order of these elements. It is therefore important to set these elements up in the correct order to produce the desired results.
+
+There are 3 different coordinate systems in Mapnik.
+- lat/lon coordinates where geometric objects placed.
+- x/y coordinates after map projection applied where you set bbox/envelope.
+- pixmap x/y coordinates used in pan function.
+
+## Further Reading
+
+- [[SymbologySupport]]
+- [[GettingStartedInPython]]
+- [[Mapnik API]] 
+
+---
+Back to [[LearningMapnik]]
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