Multi-string data-set without z layer, applying ordinal values as a workaround

Question

I'm new to GIS and have been learning a lot over the last few weeks, however, I've finally come to a point where I could use some help.

I'm working with the pdx_streets data-set from http://www.civicapps.com, which doesn't include a z-layer or elevation relating to the rendering order for ramps, overpasses, tunnels, bridges, etc.

This data-set does include F and T ordinal values(-2 to 5), which can be applied as a work-around; but what is the best way to apply this?

Currently, I have all of the street styles entered, one solution would be list each value and apply using the render order, however, this would create a lot of duplication for each style.

QGIS 2.10

Metadata: http://www.portlandmaps.com/metadata/index.cfm?&action=DisplayLayer&LayerID=52058

OS: Ubuntu 14.04

Answer 1

If I've understood the problem correctly, you can use symbol levels to achieve this.

I'm attaching a simple example where I want to colour points based on an integer attribute. By selecting symbol levels, the points are styled according to the value and the order of drawing also depends on the same value. The smaller the number the "lower" it appears in the rendered image:

You can use a similar approach to draw road segements in their z-order. You could use either the F or T attribute or take the average of the two and create a new pseudo-z attribute for styling.