Geoprocessing

Geoprocessing refers to methods employed to extract information and insights from an initial set of datasets. This exercise explores some of these methods.

Overlays

Overlay analysis combines two or more datasets and applies a certain procedure for the common areas (those that intersect) and a different procedure for the non common areas (those that are disjoint).

Resources

This exercise uses the same dataset used for the *Spatial relationships. If you need to download the data again just clik on this link. The dataset contains the following layers:

  • dorset_cadaster.qgz a QGIS project preloading a geopackage containing the following layers:

    • roads (road network)

    • water_plan (area a water management plan where special provisions may apply)

    • power_cable_(plan) (proposed route for a high voltage aereal cable)

    • parcels (the cadaster)

    • land_use (land uses as of 2015)

    • parish (admninistrative boundary of the parishes within the Dorset municipality - Tasmania)

    • party (fictional list of parties)

    • building (empty layer of type polygon)

    • topographic_map (a sample topographic map generated from Open Street Map)

    • building_type (fictional list of types of buildings)

In additon to the project and respective datasets, there are also folders with auxiliary files the exercise may refer to.

  1. Task From the Processing toolbox, search for tools to perform overlay operations to answer the following questions:

    • Extract the locations where the roads will be intersecting with the power_cable_(plan) [hint: check the Line intersections tool];

    • Extract the area of the parish that is not restricted by the water_plan [hint: check the Difference tool];

    • Extract the area of the water_plan that is not overlaps the parish [hint: check the Difference tool tool];

    • Extract the non overlapping areas of water_plan and parish [hint: check the Symmetrical difference tool];

    • Extract the parcels according with the boundary of the water_plan [hint: check the clip tool].

Geometry operations

Geometry operations usually operate on one single dataset constructing a new geometry from it.

  1. Task From the Processing toolbox, search for tools to perform geometry operations to to obtain these new layers:

    • Extract the areas within 25m from where the power_cable_(plan) [hint: check the Buffer tool];

    • Extract the all the vertices from the parcels [hint: check the Extract vertices tool];

    • Group the parcels according to the type of tenure [hint: check the Dissolve tool].

Analysis

Analysis seek to produce previously unknown information from the data we have. The next task provides an example of such analysis.

  1. Task From the Processing toolbox, search for tools to perform geometry operations to to obtain these new layers:

    • Extract the areas within 25m from where the power_cable_(plan) [hint: check the Buffer tool];

Challenge

You can combine these tools and obtain answers to complicated problems. Read the problem formulation and try to come up with a solution using one or more of the tools you experimented so far.

The power_cable_plan represents the proposed route for a necessary high voltage connection. It is still under discussion and as an input for that discussion you are asked to determine how much land per parcel * would have to be expropriated given that around each post a 10m security area is required by law*

[hint: you will need to use the Extract vertices, the Buffer and the Overlap analysis tools.