There are several options to do this:
Create a new line-layer, toggle editing, activate snapping and draw a line by snapping to start- and endpoint.
Use this expression with Geometry generator or Geometry by expression (see here how):
make_line (start_point ($geometry),end_point ($geometry))
Create a virtual layer with this query:
select make_line (...
If you want to create this sort of thing, then there is a way. I am assuming you have already broken the transects at the river. Looks like you have.
Convert the watershed polygon to a line. This creates a polyline boundary. You can use Vector - Geometry - Polygons to Lines
Vector - Geoprocessing Tools - Buffer the boundary by a small amount so that the ...
The qml file style file you get when exporting layer styles is different from the one you get in the "Style manager" when you export. The second format is the accepted one in "Create categorized renderer from style"
What is missing is a script to get "Style manager" compatible file from an existing layer style. I've made a ...
The order of layers in QGIS Layer Panel determines what will be shown on top. Drag your raster layers to the bottom in the layers panel.
This is your layers panel:
Or if you really would like to have rasters on top, then make them partially transparent so that you can see through them.
I would recommend "Point displacement" renderer. You can combine it with your existing categorized renderer. I invite you to play a little with the settings to get your personal optimized result:
Alternatively you could also try "Point cluster" renderer.
Each of the options you mentioned have their pros and cons. If using the stacked symbology approach, you may consider setting the symbol levels and making the symbols progressively larger towards the bottom of the stack. With careful symbol selection it is possible to avoid implying quantitative significance. Alternately, you may consider applying an offset ...
If you have one line layer for the contour and one straight line called 'distance', split the contour layer with the 'distance' line. Then you have a new 'contour_split' layer with three segments: one between the intersecting points and each before and after the points.
Then create line intersection points that create a layer called 'points'. Now the segment ...
Run Zonal Statistics As Table (or the QGIS equivalent) on your vector layer to get the min and max per polygon. Select polygons where min is not equal to the max (i.e. these polygons cover multiple raster values). Clip the raster based on these polygons, and then polygonize this clipped raster. Merge the resulting polygons back with the original polygons ...
Eventually I found the simple and effective way. The expression
overlay_nearest( @layer ,
limit:= 40 )
will return true if in a radius of 1000 layer units there is at least ...
Maybe this would be the complete work-flow (as partially mentioned already by @Aaron and @user2856):
make a copy of your original raster (so that extent, resolution, CRS etc. remain the same)
use GDAL > Vector Conversion > 'Rasterize (Overwrite With Attribute)' tool (gdal:rasterize_over) to overwrite the raster's values with the values from your ...