Geospatial multiple layer analysis: vector operation

common operations used to combine information from various overlain datasets

Union, intersection, symmetrical difference, and identity

Error propagation

arises when inaccuracies are present in the original input and overlay layers and are propagated through to the output layer. These errors can be related to positional inaccuracies of the points, lines, or polygons.Can arise from attribute errors in the original data table(s). Error propagation represents a common problem in overlay analysis, the impact of which depends largely on the accuracy and precision requirements of the project at hand.

slivers

common error produced when two slightly misaligned vector layers are overlain. This misalignment can come from several sources including digitization errors, interpretation errors, or source map errors.

identity ("minus") overlay method

creates an output layer with the spatial extent of the input layer. The input layer can be points, lines, or polygons. The identity layer must be a polygon dataset.

polygon-in-polygon overlay operation

employs a polygon input and a polygon overlay. This is the most commonly used overlay operation. Using this method, the polygon input and overlay layers are combined to create an output polygon layer with the extent of the overlay. The attribute table will contain spatial data and attribute information from both the input and overlay layers

intersection overlay method

employs the AND operator. An intersection requires a polygon overlay, but can accept a point, line, or polygon input. The output layer covers the spatial extent of the overlay and contains features and attributes from both the input and overlay

union overlay method

employs the OR operator. A union can be used only in the case of two polygon input layers. It preserves all features, attribute information, and spatial extents from both input layers. This overlay method is based on the polygon-in-polygon operation

symmetrical difference overlay method

employs the XOR operator, which results in the opposite output as an intersection. This method requires both input layers to be polygons. The output polygon layer produced by the symmetrical difference method represents those areas common to only one of the feature datasets

erase geoprocessing operation

essentially the opposite of a clip. Whereas the clip tool preserves areas within an input layer, the erase tool preserves only those areas outside the extent of the analogous erase layer. While the input layer can be a point, line, or polygon dataset, the erase layer must be a polygon dataset

cluster tolerance

forces nearby lines to be snapped together if they fall within a user-specified distance. Care must be taken when assigning cluster tolerance. Too strict a setting will not snap shared boundaries, while too lenient a setting will snap unintended, neighboring boundaries together

spatial join

hybrid between an attribute operation and a vector overlay operation. results in the combination of two feature dataset tables by a common attribute field. relationship is explicitly based on the property of proximity or containment between the source and destination layers, rather than the primary or secondary keys.

polygon-on-line overlay operation

opposite of the line-in-polygon operation. In this case, the polygon layer is the input, while the line layer is the overlay. The polygon features that overlay these lines are selected and subsequently preserved in the output layer.

polygon-on-point overlay operation

opposite of the point-in-polygon operation. In this case, the polygon layer is the input, while the point layer is the overlay. The polygon features that overlay these points are selected and subsequently preserved in the output layer.

Overlay operations available for use with vector data

point-in-polygon, polygon-on-point, line-on-line, line-in-polygon, polygon-on-line, and polygon-in-polygon models.

point-in-polygon overlay operation

requires a point input layer and a polygon overlay layer. Upon performing this operation, a new output point layer is returned that includes all the points that occur within the spatial extent of the overlay

line-on-line overlay operation

requires line features for both the input and overlay layer. The output from this operation is a point or points located precisely at the intersection(s) of the two linear datasets

line-in-polygon overlay operation

similar to the point-in-polygon overlay, with that obvious exception that a line input layer is used instead of a point input layer. In this case, each line that has any part of its extent within the overlay polygon layer will be included in the output line layer, although these lines will be truncated at the boundary of the overlay

overlay

the process of taking two or more different thematic maps of the same area and placing them on top of one another to form a new map that combines not only the spatial features of the dataset but also the attribute information as well.

split geoprocessing operation

used to divide an input layer into two or more layers based on a split layer. The split layer must be a polygon, while the input layers can be point, line, or polygon.

clip geoprocessing operation

used to extract those features from an input point, line, or polygon layer that falls within the spatial extent of the clip layer. all attributes from the preserved portion of the input layer are included in the output. If any features are selected during this process, only those selected features within the clip boundary will be included in the output.