Notice that your example is using two separate 2D images to convey 3D information to the reader.
This very much reminds me of European projection:
Instinctively, I would have called it "a case of European projection".
However, Wikipedia lists a more generalized name:
An oblique projection is a simple type of graphical projection used for producing pictorial, two-dimensional images of three-dimensional objects:
- it projects an image by intersecting parallel rays (projectors)
- from the three-dimensional source object with the drawing surface (projection plan).
In both oblique projection and orthographic projection, parallel lines of the source object produce parallel lines in the projected image.
Pedantically, the lines that are drawn on your example image are not parallel. However, please note that the page I linked refers to engineering drawing, which are often used as blueprints and need to be pedantically precise.
Your example image is precise on the left image (it notes dimensions etc.), but the right image seems to be a visualization, not a blueprint. Therefore, there is less need for parallel lines as the right image is not intended to convey precision.
If the image you linked is not representative of the whole tunnel, but rather a specific segment of it, the same Wikipedia page lists a second option:
Projected views (either Auxiliary or Multiview) which show a cross section of the source object along the specified cut plane. These views are commonly used to show internal features with more clarity than may be available using regular projections or hidden lines.
I think the image you linked exactly fits the definition of a section view, but I would instinctively refer to it as an oblique projection.
The reason for this is the meaning of the terms.
- "Section view" reveals that it is a "slice" from a larger part.
- "Oblique projection" focuses on the projection method that is used, rather than whether the shown object is a slice of a larger object or not.
What do you call a 2D map that shows the characteristics of a 3D train tunnel?
The most accurate answer to this question would be "oblique projection", as your generalized question also allows for images that are not section views (but are still oblique projections!)