+/* Rendering levels */
+/**
+ * GIS_LEVEL_BACKGROUND:
+ *
+ * The level used to draw background objects (stars, atmosphere, etc).
+ */
+#define GIS_LEVEL_BACKGROUND -100
+
+/**
+ * GIS_LEVEL_WORLD:
+ *
+ * The level used to draw world objects. This is for both surface data as well
+ * as things in the air or underground. Most objects should use
+ * %GIS_LEVEL_WORLD;
+ */
+#define GIS_LEVEL_WORLD 0
+
+/**
+ * GIS_LEVEL_OVERLAY:
+ *
+ * The level used to draw screen overlays. These will be drawn in front of most
+ * of ther objects. Text and markers should use %GIS_LEVEL_OVERLAY.
+ */
+#define GIS_LEVEL_OVERLAY 100
+
+/**
+ * GIS_LEVEL_HUD:
+ *
+ * The level used to draw the Heads Up Display. This is for things that are not
+ * anchored at all the the world. They should be drawn in front of everything
+ * else.
+ */
+#define GIS_LEVEL_HUD 200
+