# QZone

A **QZone** item is a 2D region represented by a hierarchical grid of squares that fit together to cover a region.

**Note: **The **Q** in **QZone** stands for "Quadtree".

This is a very compact and fast way to store and analyse complex regions. Each square can be divided into four quadrants and each quadrant sub-divided into quadrants repeatedly until they are uniform or the basic resolution of the data is reached.

For example:

Because the squares that make up the **QZone** are regularly sized, it is an extremely efficient way for the computer to model a 2D region.

Detecting whether a point is inside a large **QZone** is hundreds of times faster than detecting whether the point is inside an equivalent Polygon item.

A drawback of using **QZone** items is they have jagged edges (especially when zooming in). When you create a **QZone** you can specify the size of the smallest square. By picking a small value you can stop the **QZone** appearing too jagged.

Also see: Creating Polygon Items - Making large Polygons more efficient: QZones

## Properties

**Area**: _area#

The area covered by the item in square metres.**Clockwise**: _bClockwise&

Is the item geometry defined in a clockwise direction?**Data size**: _sizeData&

The number of bytes used to store the QZone squares.**Normalised**: _normalised&

Is the QZone normalised? All**QZone**items are created normalised, but if you move them they become de-normalised.

Before**QZone**items can be combined in Boolean operations with each other they must be normalised. When they are normalised their squares overlap. If SIS needs a**QZone**to be normalised for a Boolean operation then it will normalise it on-the-fly. But you can speed up Boolean operations by normalising**QZone**items after moving them.**Resolution**: _resolution#

The resolution of a Polygon, QZone, or Bitmap item.- For a
**Polygon**item, the value is the resolution of the invisible cached**QZone**item. If there is no cached**QZone**item then the**Polygon**item's resolution is reported as zero.

A**QZone**item is made up of progressively smaller squares. Its resolution is the size of the smallest**QZone**square.

The resolution of a**Bitmap**item is the size of each pixel. **Splinter factor**: _splinter#

The splinter factor of the Polygon. A circle has a splinter factor of 1. A very long and thin area could have a splinter factor of 100.**Polygon**items with large splinter factors are often produced by overlapping lines which are almost but not quite the same.

**TIP: **When defining a cell size for a **QZone**, you need to make a compromise between polygon accuracy and the speed of the query. Try and match the cell size to the capture scale of the data to obtain as accurate a match as possible.