HAS-QGIS-scripts

Raster Boxplot for QGIS

A QGIS Processing script that mimics GRASS’s r.boxplot. It draws a boxplot of raster values, optionally grouped by categories from a zonal (categorical) raster, and renders it in an interactive matplotlib window inside QGIS.

Features

• Boxplot of a single raster, or grouped boxplots by zones from a second raster.
• Zone ordering: natural, by ascending median, or by descending median.
• Notches, outlier toggle, whisker IQR multiplier, horizontal orientation.
• Rotated category labels, adjustable font size and DPI.
• Optional sampling for large rasters (fraction of valid cells).
• Fill boxes with the zonal raster’s color table (-c equivalent); the median line automatically shifts lighter or darker to stay readable.
• Interactive matplotlib window with pan, zoom, and save toolbar, or export to PNG / PDF / SVG.

Requirements

• QGIS 3.x with the Processing framework (bundled).
• Python packages: numpy, matplotlib, gdal, PyQt5 — all shipped with standard QGIS installations.

Installation

1. Download raster_boxplot.py from github
2. In QGIS, open the Processing Toolbox (Ctrl+Alt+T).
3. Click the Python icon at the top of the toolbox and choose Add Script to Toolbox….
4. Select raster_boxplot.py.

The algorithm appears under Scripts → Raster plots → Raster boxplot.

To update the script later, edit it in place (right-click → Edit script) or re-add it via the same menu.

Usage

Open the algorithm and set:

• Input raster — the raster whose values you want to summarize.
• Zonal raster (optional) — a categorical raster; one box per category.
• Zone ordering — natural, ascending median, descending median.
• Flags for horizontal boxes, notches, outliers, grid, whisker range, etc.
• Color boxes from zonal raster color table — uses the zones layer’s current QGIS style (paletted or singleband pseudocolor) or its embedded GDAL color table.
• Output image (optional) — leave empty for an interactive window, or provide a path to save as PNG, PDF, or SVG.

Notes

• The zones raster must share shape (rows × columns) with the input raster. If not, align them first with Processing → Align rasters.
• For very large rasters, set Sample fraction to a value between 0 and 1 so only that share of valid cells is used.
• When zonal colors are enabled but the zones layer has no palette or style, boxes fall back to gray with a warning in the log.

AUTHOR

Paulo van Breugel, HAS green academy, Innovative Biomonitoring research group, Climate-robust Landscapes research group

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