Z-order refers to the order of multiple overlapping objects in a diagram.
The actual number assigned to a particular place in the Z-order is sometimes known as the z-index.
An object with a Z-index of 1 will appear behind an object with a Z-index of 2 or greater. In other words, 1 is at the bottom of the stack or the furthest back.
In SmartDraw, there are two kinds of Z-orders to consider: shapes and layers.
Changing the Z-Index of Shapes
Any group of symbols can arranged using the commands "Send to Back" and "Bring to Front". This is outlined in this article: https://smartdraw.zendesk.com/hc/en-us/articles/360042760411-Changing-the-order-of-shapes
Clicking on Shape B and choosing "Bring to Front" will change its Z-index of 2 to a Z-index of 3. It will also move shift Shape A down into Z-index 2.
Next, select Shape B again and choose "Send to Back" to switch its X-index from 3 to 1.
Changing the Z-Index of Layers
When you're dealing with layers, you can modify their Z-order using the "Define Layers" option under Page->Layers->Define Layers. Here, you can move a layer up or down and change its Z-index.
In the above, objects in Layer 1 would appear on top of objects in Layer 2 and 3. So if an object occupied the same coordinate space in both Layer 1 and 2, the object in Layer 1 would be visible while the one in Layer 2 would be obstructed. If you need to change that order, you can select Layer 2 and click on "Move Layer Up" or select Layer 1 and choose "Move Layer Down" both would accomplish the same thing.