Spatial Projects SQL (spatialSQL)
for MapInfo Professional®

Advanced spatial query and update

  Applications of the Median Line update operator

The median update operator in conjunction with:

  •   intersects or    disjoint query,
  •    Where Clause,
  •    proximity qualifier
  •   within distance tolerance  

provides a method of creating median lines or polygons. A median line is the line which is equidistant at all points from the nearest point on the objects from which it was created.

There are many applications for median lines including:

  • Creating street centrelines from cadastral boundaries;
  • Creating median maritime boundaries between countries;
  • Trim catchment areas to the median line version;
  • Creating median lines between selected point, line or region objects.


Street Centreline Example

The combine operator is used to create casements from cadastral data

Centrelines are then created automatically from the casements and a nominated search width.

Catchment Area Example

Median Update supports a range of applications including the clipping of catchment areas.




Maritime boundary generation.

There are a number of important provisos detailed in the documentation but a good approximation to economic and territorial boundaries can be produced.


Arbitrary Selected Objects

Create median lines between any selected objects


The median boundary between polygons is derived from the buffered boundary. The edge match between the new boundaries will be exact but the generated boundary nodes will not be recreated at the same location as the original polygon.

Attributes attached to the buffered polygons are preserved in the median update version.

See a movie of the operation


Buffer - Preserving Original Polygon Boundaries

Input polygons with some boundaries touching.

MI Pro:Uniform buffer of each object.


 set table 1


 zero buffer


 run the update










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Last modified: Mar24, 2008