Create a buffer zone for each object extending outward by the given distance and including the original object. For areas, this is an outer buffer zone.
Units used for the distance value in the source / argument box are taken from the projection of the drawing. If the drawing is in Latitude / Longitude projection the units will be degrees. If the drawing is projected, the units will be in meters or feet. It is therefore strongly recommended that the drawing be projected first so that meters or other linear measure can be used instead of attempting to use degrees as a measurement unit.
To see which units are defined for the drawing's projection, click on the Tracker tool and make some measurements. Whatever units are used to show the result of the tracker tool are the units currently in force. The tracker tool is also useful for estimating the desired size range of the buffer zone.
If the drawing uses degrees and meter-based creation of buffer zones are desired, first re-project the drawing into any convenient meter-based projection (such as Orthographic) so that meters will be used as the units of measure.
See the Transform - Border Buffers topic for a detailed example illustrating the creation of buffer zones.
Buffer Zone Variations
The transform toolbar provides four different buffer zone variations.
Variations are shown based on the area shown above in blue dotted style. All variations were created by showing the resultant buffer zone area as a 50% transparent layer in a map.
The Buffers operator creates an outer buffer zone, extending 15000 meters outward from the boundary of the area and including the original area.
Inner buffer zone, comprising all parts of the original area except those extending 15000 meters inward from the boundary of the area.
Border buffer zone, extending both inward 15000 and outward 15000 from the boundary of the area.
The Common Buffer transform operator is like Buffers, but creates one buffer zone about all objects in the scope.
In the example above the green areas were created with Buffers using the lines and the blue area was created with Common Buffer. Note that there are three area objects in the case of the green buffer zones but only a single area object in the case of the common buffer.
Local Scale and Units of Measure
Stating that the units used by buffer operators are the units used in the projection is actually an oversimplification. More accurately, the parameter value is taken as the number of local drawing units. Local drawing units are normally the same as the units used by the projection. Local drawing units are the projection units multiplied by the Local scale value for the coordinate system specified in the Edit - Change Projection dialog.
Because the Local scale value is usually 1, the value used in the source / argument box for buffer operators is usually the same number in local drawing units. Entering 1500 in a meter-based projection thus means 1500 meters. However, if the Local scale value is not 1, the value in the source / argument box must be multiplied by the Local scale value to get the number of units that will be used to create the buffer. If the Local scale value is 10 in a meter-based projection, for example, then entering 50 into the source / argument box is not a command to create a 50 meter buffer, it is a command to create a 500 meter buffer.
An additional subtlety must be considered when this transform operator is used with a drawing layer within a map. If the map component's projection is degree based while the native projection for the drawing is meter based (as, for example, with the Orthographic projection) or vice versa, then the transform operator will use whatever units are used by the drawing's projection.
Tech Tip
Variations on the basic buffer zone constructions with areas may be easily created by first creating a buffer zone and then using Clip with (Intersect) or Clip with (Subtract) between the new buffer zone area object and the original area object. For example, using a Clip with (Intersect) between a border buffer and the original area will produce a zone that consists only of the defined distance within the area's boundary and that excludes the more inner regions of the original area as well as everything outside of the boundary.
The buffer distance used must be at least four times the size of the location precision factor. If precision has been set to 10 meters then the buffer distance must be larger than 40 meters.
See Also: