extend package documentation

mapping/doc.go

@@ -1,4 +1,14 @@
 /*
-Package mapping provides functions for defining and executing the database schema.
+Package mapping provides implements mapping and convertion between OSM elements and database tables, rows and columns.
+
+The core logic of Imposm is accesible with the Mapping struct.
+A Mapping creates filters and matchers based on mapping configuration (.yaml or .json file).
+
+Filters are for initial filtering (during -read). They remove all tags that are not needed.
+
+Matchers map OSM elements to zero or more destination tables. Each Match results can convert an OSM element
+to a row with all mapped column values.
+The matching is dependend on the element type (node, way, relation), the element tags and the destination
+table type (point, linestring, polygon, relation, relation_member).
 */
 package mapping