Defines the draw order of a graphic. Graphics with higher Z-index values are drawn on top of lower Z-index graphics. A graphic's Z-index is mostly relevant for display in a two-dimensional map view. For dynamic 3D rendering (in a scene view), graphic display order is determined by the distance to the camera rather than by Z-index. The Z-index is considered, however, when using static rendering in a scene view (draping graphics on the surface, in other words).
If Z-index is not set, graphics will usually render in the order in which they were added to the graphics overlay, the first added is rendered first and subsequent ones on top. In rare cases, the rendering algorithm may change the display order to provide more efficient rendering. If ordering is important, set the Z-index explicitly on graphics. You can also place graphics of the same geometry type in their own graphics overlay and manage the order of the overlays in the MapView or SceneView.