Add references to general aggregation documentation in MapConfig spec

docs/MapConfig-Aggregation-extension.md

@@ -22,7 +22,7 @@ The value of this attribute can be `false` to explicitly disable aggregation for
         // * "point-sample", the default places geometries at a sample point (one of the aggregated geometries)
         // * "point-grid" places geometries at the center of the aggregation grid cells
         // * "centroid" places geometriea at the average position of the aggregated points
-        // See https://github.com/CartoDB/Windshaft-cartodb/blob/master/docs/... for more details
+        // See https://github.com/CartoDB/Windshaft-cartodb/blob/master/docs/aggregation.md#placement for more details
         placement: "point-sample",
 
         // OPTIONAL
@@ -33,6 +33,7 @@ The value of this attribute can be `false` to explicitly disable aggregation for
         // is always generated in addition to the defined columns.
         // The column names `cartodb_id`, `the_geom`, `the_geom_webmercator` and `_cdb_feature_count` cannot be used
         // for aggregated columns, as they correspond to columns always present in the result.
+        // See https://github.com/CartoDB/Windshaft-cartodb/blob/master/docs/aggregation.md#columns for more details
         columns: {
             "aggregated_column_1": {
                 "aggregate_function": "sum",
@@ -43,10 +44,12 @@ The value of this attribute can be `false` to explicitly disable aggregation for
         // OPTIONAL
         // Number, defines the cell-size of the spatial aggregation grid as a pixel resolution power of two (1/4, 1/2,... 2, 4, 16)
         // to scale from 256x256 pixels; the default is 1 corresponding to 256x256 cells per tile.
+        // See https://github.com/CartoDB/Windshaft-cartodb/blob/master/docs/aggregation.md#resolution for more details
         resolution: 1,
 
         // OPTIONAL
         // Number, the minimum number of (estimated) rows in the dataset (query results) for aggregation to be applied.
+        // See https://github.com/CartoDB/Windshaft-cartodb/blob/master/docs/aggregation.md#threshold for more details
         threshold: 500000
     }
 }