3.3 Overlay units - LUPMISManual

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3. GIS operations

3.3 Overlay Units

Level of expertise required for this Chapter: Advanced; general Map Maker training

When processing and modelling GIS, there is a strong need for overlaying and processing two or more layers.

In Map Maker, the main utility to overlay is the Intersect/Unite option: Main menu > Utilities > Vector utilities > Intersect / Unite files > Intersect lines and polygons window: Add file > Select folder > Select the file, which you want to overlay > Open > … Repeat, if you have more than one file … > Tick ‘Find intersections’ > Tick ‘Tidy boundaries’ > Snap distance: 0 m > Execute > Save result as > Specify new temporary file name for output > Save > Quit

This output file can then be edited in the live layer.

Be aware, that all layers have to be ‘clean’, i.e. adjacent, i.e. snapped before the operation, and not like the example below:

In a scenario like below, you either have to make them adjacent first or – preferably – through the Intersect option.

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For example: You have two polygons in two different layers (DRA files) and are interested in the overlay:

  • A: Either, result of 3 polygons: Area 1 only (right diagonal), area 2 only (left diagonal), and overlap area (hatch)

  • B: Or, result of 2 polygons: Original area 1 (right diagonal plus hatch) and area 2 without the area covered by the other unit (left diagonal)

  • C: Or, only the overlap area (hatch)

In the Intersect lines and polygons window (as explained above), you select these two layers (1, see below), click the two boxes (2) and execute (3), then quit (4).

For requested output B, you have to join the two left polygons with the Join-tool, for output C you tick the option ‘Only keep polygons common to all files’.

If you like to maintain style numbers and/or labels and/or attribute data, you have to create 'seeds' from a selected layer (see  Chapter 4.6).

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Alternatively, there are overlay functionalities through the Action window:

  • Either through right-mouse > Live layer options >

  • Or through: Selection Manager > Select-tool (at toolbar left) > Actions > Polygon manipulation > Join adjacent polygons of the same style / ID / display label > OK

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If there is any technical problem with the Intersect module, as described below, use the external module Intersect.exe in folder C:\Map Maker (see installation  Annex 1.1.1).

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Note: Following summary table lists the operations understood under overlay procedures in GIS. (Some of the terminology is specific for ESRI products).


Combine polygons from one or more layers to create one new layer with all polygon areas from all input layers

- If adjacent: (Snap and) Join
- If overlapping: Intersect/unite > Join
- If not connected: Possible, but not recommended


Overlay polygons from one or more input layers to create one new layer, preserving only the area of overlap

- If one layer: Intersect/unite > Delete non-overlapping units
- If two or more layers: Intersect/unite (with tick on ‘Only keep polygons common to all files’)


Delete polygons



Combine polygons from two or more input layers to create one new layer



Break a polygon into two

Cutter-tool (see Chapter 2.8 for the procedure to split a polygon)


Trim a polygon in one layer according to the boundaries of another layer

Selection Manager > Trim vectors to polygons
(see Chapter 3.6
for the procedure to clip)


Create polygon of maximum distance around a feature

Selection Manager > Generate buffer zones
(see Chapter 3.1
on how to buffer)


Exclude one polygon from another polygon

- If partly overlapping: Same process as ‘Intersect’ above
- If ‘island’: Intersect/unite > no need to delete (see also Chapter 2.14
for the procedure to insert an island)

Combine (ESRI)

Combine polygons to create one common polygon, excluding the area of overlap

Intersect/unite > Delete area of overlap > Join

Union (ESRI)

Combine two or more polygons to create one common polygon, disregarding any overlap

See under ‘Union’ above

Emphasis is put in this listing on overlaying polygons, but similar overlays can be done also for lines and points.


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