QGIS Data Visualization
Raster Data
- Launch QGIS by clicking on the QGIS option in your start menu programme
- Go to the Layer menu and select Add Raster Layer
- Browse to the folder where you have kept the sample data and go to Raster folder (Example: D:\sw\QGIS\Quantum GIS Lisboa\GIS DataBase\qgis_sample_data\raster and select landcover.img)
- If the file is not visible in the folder, select [GDAL] Erdas Imagine (*.img *.IMG) file type format at the bottom of the box and select the layer
- Click Open button
If you have followed the steps correctly, you will be able to visualize the raster data as shown below:
Use zoom-out, zoom-in, and pan buttons to go to your particular area of interest.
To change the colour style of the raster layer, right click on Landcover Layer in the layer box then:
- Select Properties
- Click on Style tab, change the Colour map to Pseudocolor
- Click Apply and then click OK. The style changed raster layer appears as below:
So now you have learned with the above mentioned steps, how to visualize a single band image. You can similarly visualize a multiband image by opening it under Add Raster Layer from Layer Menu. After opening the layer you can go to Layers window, select the opened layer, right click and then select properties. It will open layer properties dialogue box. Click on Styles tab, click on Three band color check box and select any three bands you want to visualize under Red, Green and Blue band options as shown below:
Vector Data
- Again click on Layer menu and select Add Vector layer
- Let File as default source type
- Browse to select the vector layer in the same location in gml folder. For example: (E:\sw\QGIS\Quantum GIS Lisboa\GISDataBase\qgis_sample_data\shapefiles\rivers.shp) and select the file rivers.shp
- If file is not visible, select any other available file
- Click Open again click open in the Add Vector dialogue box
- Click Open
You should be able to visualize the vector data rivers.shp as in below:
Use zoom-out, or zoom-in and pan buttons to go to your area of interest. To change the colour style of vector layer, right click on rivers Layer in the layer box then:
- Select Properties
- Click on Style tab, click on the dropdown box just below the style tab and change from Single symbol to Categorised
- Click on Column dropdown box and select NAM. Click on Color ramp dropdown box and select the second one, that is, BrBG
- Click Classify. This will create many numbers of symbols.
- Click Apply, check if the results look good, if yes then click OK. You should be able to visualize the vector data rivers.shp.
You can also open attribute table of the vector layer by right clicking on the layer and choosing Open Attribute Table.
You have learnt about QGIS data visualization. Now let’s take a look at how to import and export raster and vector data.
Importing/Exporting Data
In QGIS, a variety of different formats of raster and vector data can be directly visualized. Data and project files can be imported or exported into different formats through following plugins:
GPS Tools: Used for loading and importing GPS data by selecting GPS->GPS Tools from Vector menu
SPIT: It is used to import Shape file to Postgre SQL/PostGIS by selecting Import Shapefile to PostgreSQL -> SPIT from Database menu
Mapserver Export: It is used to export QGIS project file to a MapServer map file by selecting Mapserver Export -> Mapserver Export from Web menu.
Add Delimited Text Layer: It is used to import spreadsheets or CSV file formats into QGIS by selecting Add Delimited Text Layer from Layer menu.
Related content: Guide to installing QGIS in your computer
