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spatialthoughts / qgis-tutorials

Source files for sphinx-based website
http://www.qgistutorials.com
Apache License 2.0
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Basic Raster Styling and Analysis (QGIS3) — QGIS Tutorials and Tips #150

Closed utterances-bot closed 6 months ago

utterances-bot commented 6 months ago

Basic Raster Styling and Analysis (QGIS3) — QGIS Tutorials and Tips

https://www.qgistutorials.com/en/docs/3/raster_styling_and_analysis.html

svelkus commented 6 months ago

Thank you for this straightforward and clean tutorial. This is a easy to understand example of using the raster calculator and hopefully will build confidence in the use of this tool.

MTrang252 commented 5 months ago

Hello, the min and max value of the population change are -34398 and 187927 after using raster calculator respectively (step 14). However, these values become -160 and 951 at step 15. Could you explain this? Thank you.

spatialthoughts commented 5 months ago

@MTrang252 In Step 15, we choose to style the layers with a Cumulative count Cut with values at 2- and 98-percentiles and use them at minimum and maximum. This is used to remove outliers in your data which may have very high or low values.

Donsodiq commented 3 months ago

Thank you:) Question: If we choose a resolution lower than the one used in this tutorial, can we still achieve the same output?

Donsodiq commented 3 months ago

Also, I don't understand why the classes were deleted at first and how they were regenerated again. I am referring to the "Population changes 2010_2000" variables where we hold the shift key. Thank you

spatialthoughts commented 2 months ago

@Donsodiq You can use any resolution of population dataset. There are many higher resolution and updated datasets available. Please see this presentation on Introduction to Gridded Population Datasets from one of my courses to know more.

Regarding why the classes were deleted first - it is because when you select a color ramp, a default symbology with the chosen distribution is applied and some classes are created automatically. Since the purpose of the tutorial was to visualize areas with growth, decline and no-change, we deleted the default classes and created our own.

darrylvil commented 3 weeks ago

Hi...how did you chose the upper bounds values? (-100, 100, 1000 and 100000 as the upper-bounds)?

spatialthoughts commented 3 weeks ago

@darrylvil Looking at the distribution of the data, these seemed sensible ranges for to capture areas of low and high growth. You can look at the resulting values rising the Identify tool to see what the values are for high-growth cities vs. low-growth areas and decide.