QGIS – Managing Large Data Files (Vector & Raster) in QGIS 3

data managementqgis

I work for a local authority so use data covering a large area. Therefore some datasets I use become large and cumbersome.

For example I have a vector layer for contours and a raster layer for hillshade. As I am relatively inexperienced I created Booth of these of a series of tiled points and created a single file. I am happy with the results but performance is slower.

What are the main options available to improve the performance of the vector layers for a single user on one PC and for a team? This should allow me to both display and analyse the data efficiently.

What are the main options available to improve the performance of the raster layer?

Best Answer

For your contours, you can

use simple scale dependent visibility to turn the layer off when zoomed out too far
build a spatial index
you could also try a rule-based symbology to limit the contour interval shown as you zoom out
you may need to build an attribute index on the elevation field to help speed up any labelling and rule-based symbology

For your raster, you can

build raster overviews (pyramids)

Related Solutions

[GIS] Poor performance with storing large rasters in PostGIS and visualising in QGIS

If you want to display large rasters in QGIS, you have to build pyramids, either for a tif image on the file system or for a image registered in Postgis.

The performance difference in QGIS rendering between a large raster in the file system or in Postgis is miminal. Users will not notice the difference. But - if and only if - you build the pyramids with the option -l.

If you simple import the image without the -l option, or with just -l 4 it will not work.

If you use, for example, -l 2,4,8,16, four levels of pyramids will be created, like in the layer below:

If you want to have a better user experience, you should add more levels of pyramids, like -l 2,4,8,16,32,64,128,256. This will create eight levels of pyramids.

To summarize, the answer to this question is: import the raster with the option -l and use the same number of pyramid levels as you use for the same raster on the file system.

For example:

raster2pgsql -s 3161 -d -C -I -M -l 2,4,8,16,32,64,128,256 D:\PostGIS_data\dem.img -t 100x100 raster.dem100 | psql -h localhost -U postgres -p 5432 -d postgres

[GIS] Speeding up the vector clip in QGIS

You could:

Simplify the geometries of your large polygon shapefile:
```
Vector > Geometry Tools > Simplify Geometries...
```
Select only those features from the large polygon shapefile which intersects the single polygon:
```
Processing Toolbox > QGIS geoalgorithms > Vector selection tools > Select by location
```
Then use these selected features for clipping by enabling the Use only selected features in the Clip tool.

Best Answer

Related Solutions

[GIS] Poor performance with storing large rasters in PostGIS and visualising in QGIS

[GIS] Speeding up the vector clip in QGIS

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