Instructions for use

The buffer function is used to generate a single buffer, which refers to a polygon of a certain width automatically created around point, line, or area entities. The generated buffer result can continue to participate in subsequent analysis operations.

• Currently, it only supports creating a buffer for point, line, and region datasets, but does not support CAD datasets, network datasets, or route datasets.
• Due to differences in data types, the parameters for creating a buffer are entirely different. For line datasets, you can choose between round or flat buffer types; for point or area data, only round buffers can be generated. When the buffer type is flat, you can create buffers with unequal left and right radii or only left or right buffers for line datasets.
• When specifying the buffer distance using the "numeric" method, region datasets allow negative values, while point and line datasets only accept positive values. However, the buffer distance cannot be zero for point, line, or region datasets.
• When specifying the buffer distance using the "field-based" method, if the specified field value for an object is null or zero, no buffer will be created for that object. For point and line datasets, if the field value is negative, it is treated as positive. When generating a flat buffer for line data, if the left (right) radius field is negative, its absolute value is used as the right (left) radius.

Function Entry

• Spatial Analysis tab -> Vector Analysis -> Buffer -> Select Buffer from the dropdown menu;
• Toolbox -> Vector Analysis tool -> Buffer Analysis -> Buffer item;

Parameter description

You can create a buffer for point/region datasets or line datasets. When creating a buffer for line data, you need to set the buffer type, which can be round or flat, whereas this is not required for point or area data. Therefore, when buffering line data, additional options appear in the "Create Buffer" dialog. Below, using line data buffering as an example, the parameters in the "Create Buffer" dialog are explained.

• Buffer source: Select the datasource containing the dataset for buffer creation.
• Buffer dataset: Select the dataset for buffer creation. Based on the data type for buffering, the system automatically filters datasets under the selected datasource, displaying only line datasets. If buffering point or area data, only point or region datasets under the corresponding datasource are shown.
• Buffer only selected objects: When objects in a dataset are selected, the checkbox before "Buffer only selected objects" becomes available. Checking this option means buffering only the selected objects, and you cannot change the datasource or dataset; unchecking it means buffering all objects in the dataset, allowing modification of the datasource and dataset for buffering.
• Round: Draws parallel lines on both sides of the line at the buffer distance and semicircles at the endpoints with the buffer radius, connecting to form the buffer area. The default buffer type is round.
• Flat: When creating a buffer, it uses the segment between adjacent nodes of the line data as one side of a rectangle and the left or right radius as the other side to generate a rectangular buffer area. For line data, when generating a Flat buffer, you can create buffers with unequal left and right distances or single-sided buffers.
  • Left buffer: Creates a buffer on the left side of the line data.
  • Right buffer: Creates a buffer on the right side of the line data.
• Union buffer: Checking this option means merging the buffers of multiple objects. Unchecking it preserves the generated buffer results without merging. As shown below, generating multiple buffers for two circles (blue). The buffer result is shown in Figure 1; when moved, it reveals that the two buffers merge into a complex object, with Figure 2 showing the merged buffer. Note: Without checking union buffer, buffers of different objects do not merge and remain separate simple objects.

Figure 1: Single buffer result	Figure 2: Merged buffer

• Display on map: Checking this option means that after buffer creation, the result is added to the current map window. Unchecking it prevents automatic addition. This is checked by default.
• Keep attributes: Checking this option means each generated buffer retains the non-system attribute fields of the corresponding original object. Unchecking it loses the non-system field attributes. This is checked by default. When Union Buffer is checked, this option is unavailable.
• Number of arc segments (4-200): Sets the smoothness of the generated buffer boundary. A higher value increases the number of arc segments, making the boundary smoother. Valid range is 4-200. Default value is 100.
• Unit: Unit for buffer distance, such as millimeter, centimeter, decimeter, meter, kilometer, inch, foot, mile, degree, yard, etc.
• Select how to specify the buffer distance.
  • Left radius: Supports direct input of the left buffer radius, selecting a numeric field to use its value as the left radius, or setting an expression to use its value as the left radius.
  • Right radius: Supports direct input of the right buffer radius, selecting a numeric field to use its value as the right radius, or setting an expression to use its value as the right radius.
• Result datasource: Select the datasource to save the generated buffer result.
• Result dataset: Enter the dataset name to save the generated buffer result. If the name already exists, an invalid dataset name prompt appears, requiring re-entry.

Notes

Regarding buffer radius: There are two setting methods, numeric and field-based.

• Numeric
  • Point and line data do not support negative radii; area data supports negative radii.
• Field-based
  • This method is only valid when buffering datasets or record sets and requires specifying a valid field other than system fields.
  • For point and line datasets, if the buffer radius field contains negative values, their absolute values are used for buffering.
  • When the buffer radius is a field or field expression: For area data, if union buffer is applied, the absolute value is used; if not merged, negative radii are processed as such.
  • When the buffer radius is a field expression: This is only valid when buffering a dataset. If the "selected objects only" option is checked, setting the buffer radius to "expression..." under "field-based" is unsupported and will result in an analysis failed prompt.

Related Topics

About buffer analysis

Create Multi-buffer