Polygons

A polygon is a closed shape which defines a specific feature by it’s outline or extent - like a country or a building. Polygons are interconnected lines between points, created at defined locations within a coordinate system. The beginning point and end point of a polygon are in exactly the same place and all the other points are unique. A polygon needs a minimum of three points (nodes) but there is no upper limit to their extent, and they can be used to accurately define very complex real-world features.

When to draw polygons – within Coasts in Mind, there are many occasions when a polygon will add useful information to a record:

• When a record relates to a specific location with a defined area or extent, which doesn’t have other visually identifying characteristics as a reference, eg not a photo which a Viewpoint would locate.
• When you are defining a building which is marked on a historic map but is no longer standing
• When you are defining a building which is still standing, but which was visibly different in the past and the changes can be recorded with a polygon. If multiple changes are visible, consider creating a record and polygon for each phase/change, and joining them together as a Collection.
• Recording a specific area or extent which can be accurately identified from landmarks, or other information visible in the platform reference materials (maps etc)

When not to draw polygons – this section will help you decide when a polygon isn’t the best way to add annotation to a record:

• When the available location information is vague, or covers a very large area, a point placed centrally within the area is more effective than a large polygon
• When a Viewpoint is better suited to define the location (eg, of an image or location within a record)

How to draw polygons – within the contribute system you will find the ‘Annotations’ tab, here you will be prompted to add additional information to your record which will display on the map under certain circumstances. Select ‘add Polygon’

• To draw a (segmented) polygon, start by left-clicking where you want to begin outlining your feature. Keep clicking with your mouse or trackpad around the feature edge, using as many clicks/points as you need to make a nice, accurate shape, keeping as close to the edge of the feature as possible. When you’ve finished drawing, just click on the first point you drew to close the polygon.
• To edit a polygon you have drawn, click the select button which is represented by a pointing finger then click on the polygon you have drawn. You can then click and drag each point to reposition them or hover over a line between points and click to add a new point.
• To delete a polygon, use the select tool to click on it. The box that opens will have the word DELETE at the bottom. Click this to delete the shape.
• If you draw multiple polygons, it may be useful to add a name and description to each to help differentiate them.