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Mapspeak or “how to tell your polygons from your vectors”

Mapping is a technical subject but that doesn’t mean that you have to learn a whole new language to understand it…!

Inevitably, there are a few key terms that are handy to know and the list below covers the most useful ones.

Links are included to expanded explanations for the curious….

 

Vector – Map data that is comprised of lines and shapes that can be altered.

Raster – Map data that can’t be altered. Often used as a backdrop to Vector data. A bit like the wallpaper on your PC.

Polygon – vector data that comprises of lines linked together to create a “sealed” shape. (e.g a field or building). A Polygon can be measured for area.

Polyline – A line (not surprisingly..!). A polyline can be measured for length. It can be joined to other lines to create a polygon.

Node – a single point (or dot) on a polyline or polygon which indicates a change of direction. Polylines and polygons can comprise of numerous nodes. Any polyline will have at least two nodes, one at each end.

Pen/Pencil – One layer in the list of map layers will have a pen/pencil symbol next to it. This layer is the Active Layer – any object that you create on the map will belong to that layer. The pen/pencil can be moved from layer to layer as required.

Importing – Adding extra map data to an existing map. Usually this is supplied from other types of mapping software. This could be RPA field boundaries, tree surveys, DXF files, Land Registry Titles, etc.

Exporting – Creating data from an existing map to supply to others who are using different software. This could be to supply an existing map as a DXF file to someone who has AutoCAD software.

Geo-referencing – linking the map co-ordinates of a map to those of the real world. Any point in Britain can be referenced using the Ordnance Survey Grid System. Ordnance Survey map data supplied by Pear complies with the O.S. Grid System and can be linked to Google Earth and used on GPS capable devices. Map data sourced elsewhere may not conform to the O.S. Grid System.

O.S. Grid System – This system divides the country into squares and each square has a unique 2 number reference. Typically this will comprise of 2 sets of 6 numbers e.g. 450325, 345100. The first number is known as the Easting, the second is the Northing.

Easting/Northing – the start point for the O.S.Grid System is 0,0 (about 50 miles west of the Isles of Scilly). If you go due East from there then your Eastings figure will increase. If you travel North then your Northing figure will also increase. If you need to find a grid reference on a map in PTMapper then place the cursor over any point on a map – the grid co-ordinates are shown at the bottom of the screen.

 

 

Updated on 21/06/2017

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