Converting between raster and vector formats allows you to make use of both raster and vector data when solving a GIS problem, as well as using the various analysis methods unique to these two forms of geographic data. This increases the flexibility you have when considering data sources and processing methods for solving a GIS problem.
To combine a raster and vector analysis, you need to convert the one type of data to the other. Let’s convert the raster result of the previous lesson to a vector.
The goal for this lesson: To get the raster result into a vector that can be used to complete the analysis.
Start with the map from the last module, raster_analysis.qgs
. There you
should have the all_conditions_simple.tif
calculated during the previous
exercises.
Click on Raster ‣ Conversion ‣ Polygonize (Raster to Vector). The tool dialog will appear.
Set it up like this:
Change the field name (describing the values of the raster) to
suitable
.
Save the shapefile under exercise_data/residential_development
as all_terrain.shp
.
Now you have a vector file which contains all the values of the raster, but
the only areas you’re interested in are those that are suitable; i.e., those
polygons where the value of suitable
is 1
. You can change the
style of this layer if you want to have a clearer visualization of it.
Refer back to the module on vector analysis.
suitable
has the value of 1
.exercise_data/residential_development/
as
suitable_terrain.shp
.Although unnecessary for our current problem, it’s useful to know about the
opposite conversion from the one performed above. Convert to raster the
suitable_terrain.shp
vector file you just created in previous step.
exercise_data/residential_development/raster_conversion.tif
;837
and 661
,
respectively.Poznámka
The size of the output image is specified here to be the same as the original raster which was vectorized. To view the dimensions of an image, open its metadata (Metadata tab in the Layer Properties).
Converting between raster and vector formats allows you to widen the applicability of data, and need not lead to data degradation.
Now that we have the results of the terrain analysis available in vector format, they can be used to solve the problem of which buildings we should consider for the residential development.