How to do intersection in QGIS?

Intersection is a vector overlay operation done by polygon intersection operator. The result of this operator is the collection of all possible polygon intersections; the attribute table result is a join of the two input attribute tables.

Objective: The main objective of this tutorial is to see the houses that would be affected by road expansion project (from Buffer analysis) and to learn intersect in QGIS.

In the last lab we did buffering of road taking distance of ‘5m’. Today we will see the no. of houses that will be affected by this road expansion project using ‘Intersection’ geoprocessing tool. 

I hope you have reached till here. Make sure your both ‘building’ and ‘road’ data are in same coordinate system ‘WGS 84/44N’. If not do Projection to convert them.

Using Intersection tool to know the houses affected.

Step1: Right click ‘44N_buildings’ -> open attribute table. 
Do the same for ‘RoadBuffer’
You will see something like this.

Step2: Go to Vector -> Geoprocessing tools -> Intersection

A window will be displayed like this.

Now adjust the following settings parameter
Step3: Keep Input layer as ‘44N_buildings’, Overlay layer as ‘RoadBuffer’, Save it to a file by clicking three dots icon in (Lab1.5/ Output) with ‘Intersect_RB’ and finally click Run.

Here we used ‘44N_buildings’ as input layer because it is the building data that we want to see being affected by ‘RoadBuffer’
 
If everything goes right you will see following output.

Step4: Right click ‘Intersect_RB’ -> open attribute table.
These are the list of houses that will be affected by the project.

How to do Buffer Analysis in QGIS?

Buffer is a spatial analysis done in GIS. It is a kind of neighborhood function which uses geometric distance to define the neighborhood of one or more target locations then determine the area around them, within a certain distance.

It can be done on both vector and raster data. The one normally done with raster data is called proximity analysis in GIS. Here I'll be using vector data.

Objective: The main objective of this tutorial is to learn buffering in QGIS. Lets say this buffering is for a road expansion project.

Step1: Load the road data ‘RoadClipped_44N in Layers panel.

 

Step2: Go to Vector -> Geoprocessing Tools -> click on Buffer 

A window will be displayed like this.
 

Now adjust the following settings parameter
Step3: Keep Input layer as ‘RoadClipped_44N’, Distance: 5, Units: meters, Save it to a file by clicking three dots icon in (Lab1.4/ Output folder) and finally click Run
 

If everything goes right you will see following output.

 Step4: Load the ‘Building_44N’ data in layers panel.

Finally, we have got our buffer.
 You can zoom in zoom out and 

Want to see the video?

See the affected houses.

How to do projection in QGIS?

Projection is the transformation of curved surface (latitude, longitude) of the earth to the flat/plane surface (XY). This allows to make a map with correct distance, area or direction. There are many different types of projection and which to use all depends on purpose of your analysis.

In this tutorial I'm going to show how projection is done in QGIS. 

For this, I will be using a boundary data of 'Siyari' VDC which is in WGS 84 (Geographic Coordinate system) and will convert it to WGS 84/ 44N (Projected Coordinate system).

Step1: Load the vector data ‘Siyari’ in Layers panel.

Step2: Double left click ‘Siyari’ layer -> Information -> under Coordinate Reference System you will see Name: EPSG:4326 - WGS 84 .

It means our data is in WGS 84 Geographic Coordinate System and we need to convert this to Projected Coordinate system. 

Converting data from Geographic Coordinate System to Projected Coordinate system

Step1: Click on Vector -> Data Management Tools -> Reproject Layer

A new window will appear where you have to  adjust some settings.

Step2: Keep Input layer as default-> click on earth icon in Target CRS

Step3: Search for 32644 in Filter menu -> click on WGS 84/ UTM zone 44 N -> click ok

Now your Target CRS will be seen as WGS 84/ UTM zone 44 N

Step4: Save it as ‘Siyari_44N’ to your desired location by clicking three dots icon in ‘Reprojected’ menu -> click Run

If everything goes fine you will get following output.

 

Now if you see its Coordinate Reference System. Now it has been changed to WGS 84/ UTM zone 44 N.

Finally, a new projected data has been obtained.

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