When drawing objects typically as polygons, two or more objects may share a common boundary. To achieve a perfect common boundary with no gaps or overlapping:
•Select the layer on which to draw the object (will need to be a Polygon Layer).
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Click on the Drawing button. The drawing Toolbar will appear in the top left hand corner of your image.
•On your map the cursor will be a hand with cross hairs. Where there is a common boundary, hover the cursor over a point that makes up part of the other object. The cursor will change from cross hairs to a hand pointing. When this happens, it means that if you left mouse click to mark a point, it will "snap" to the already existing point. Continue along the common boundary marking each point the same way as previous.
•If only part of the object has a common boundary, then to mark the remainder of the object, continue the normal drawing function with the cross hairs cursor.
•When finished either double left mouse click when marking the last point or click the Stop Drawing button 
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