Can Vector Dataset or Layer Be Overlaid on a Raster/layer Dataset in Arcgis?

7.two Multiple Layer Analysis

Learning Objective

1. The objective of this section is to go familiar with concepts and terms related to the implementation of basic multiple layer operations and methodologies used on vector characteristic datasets.

Among the well-nigh powerful and commonly used tools in a geographic information system (GIS) is the overlay of cartographic data. In a GIS, an overlayThe procedure of taking ii or more different thematic maps of the same surface area and placing them on top of 1 some other to form a new map. is the process of taking 2 or more different thematic maps of the same area and placing them on top of one another to form a new map (Figure 7.four "A Map Overlay Combining Information from Point, Line, and Polygon Vector Layers, every bit Well every bit Raster Layers"). Inherent in this procedure, the overlay function combines not only the spatial features of the dataset merely also the aspect information as well.

Figure 7.4 A Map Overlay Combining Information from Betoken, Line, and Polygon Vector Layers, also equally Raster Layers

A common example used to illustrate the overlay process is, "Where is the best place to put a mall?" Imagine you are a corporate bigwig and are tasked with determining where your visitor's next shopping mall will be placed. How would you attack this problem? With a GIS at your command, answering such spatial questions begins with amassing and overlaying pertinent spatial information layers. For case, you may get-go want to determine what areas can support the mall past accumulating information on which state parcels are for sale and which are zoned for commercial development. After collecting and overlaying the baseline information on bachelor evolution zones, you tin brainstorm to determine which areas offer the nearly economic opportunity by collecting regional data on average household income, population density, location of proximal shopping centers, local buying habits, and more. Next, yous may want to collect information on restrictions or roadblocks to evolution such every bit the cost of state, cost to develop the country, customs response to development, capability of transportation corridors to and from the proposed mall, tax rates, and so forth. Indeed, but collecting and overlaying spatial datasets provides a valuable tool for visualizing and selecting the optimal site for such a business endeavor.

Overlay Operations

Several basic overlay processes are bachelor in a GIS for vector datasets: betoken-in-polygon, polygon-on-indicate, line-on-line, line-in-polygon, polygon-on-line, and polygon-on-polygon. As y'all may be able to divine from the names, 1 of the overlay dataset must always exist a line or polygon layer, while the second may be point, line, or polygon. The new layer produced post-obit the overlay performance is termed the "output" layer.

The signal-in-polygon overlayAn overlay technique that creates an output signal layer that includes all the points occurring within the spatial extent of the overlay layer. 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 (Figure 7.iv "A Map Overlay Combining Information from Point, Line, and Polygon Vector Layers, equally Well as Raster Layers"). In addition, all the points in the output layer contain their original attribute information every bit well as the aspect information from the overlay. For example, suppose you were tasked with determining if an endangered species residing in a national park was found primarily in a particular vegetation customs. The commencement step would be to acquire the point occurrence locales for the species in question, plus a polygon overlay layer showing the vegetation communities inside the national park boundary. Upon performing the point-in-polygon overlay operation, a new point file is created that contains all the points that occur within the national park. The attribute tabular array of this output betoken file would also contain information about the vegetation communities existence utilized past the species at the time of observation. A quick scan of this output layer and its attribute table would permit you to determine where the species was found in the park and to review the vegetation communities in which it occurred. This process would enable park employees to make informed management decisions regarding which onsite habitats to protect to ensure continued site utilization past the species.

Figure 7.5 Point-in-Polygon Overlay

Every bit its name suggests, the polygon-on-point overlayAn overlay technique that creates a polygon layer from those input polygons that overlay features in a point layer. operation is the reverse of the point-in-polygon operation. In this instance, the polygon layer is the input, while the indicate layer is the overlay. The polygon features that overlay these points are selected and subsequently preserved in the output layer. For instance, given a point dataset containing the locales of some type of crime and a polygon dataset representing city blocks, a polygon-on-betoken overlay performance would allow police to select the urban center blocks in which crimes have been known to occur and hence decide those locations where an increased police presence may be warranted.

Effigy 7.6 Polygon-on-Point Overlay

A line-on-line overlayAn overlay technique in which output from this functioning is a betoken(s) located at the intersection(s) of the two linear datasets. performance requires line features for both the input and overlay layer. The output from this operation is a signal or points located precisely at the intersection(s) of the 2 linear datasets (Effigy 7.seven "Line-on-Line Overlay"). For example, a linear feature dataset containing railroad tracks may be overlain on linear route network. The resulting indicate dataset contains all the locales of the railroad crossings over a town'south road network. The aspect tabular array for this railroad crossing point dataset would contain information on both the railroad and the road over which it passed.

Figure 7.vii Line-on-Line Overlay

The line-in-polygon overlayAn overlay technique in which each line that has any part of its extent inside the overlay polygon layer will be included in an output line layer. operation is similar to the point-in-polygon overlay, with that obvious exception that a line input layer is used instead of a indicate input layer. In this example, 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 (Figure vii.9 "Polygon-on-Line Overlay"). For case, a line-in-polygon overlay tin can have an input layer of interstate line segments and a polygon overlay representing city boundaries and produce a linear output layer of highway segments that autumn within the city boundary. The aspect table for the output interstate line segment will contain information on the interstate name as well equally the city through which they pass.

Figure 7.8 Line-in-Polygon Overlay

The polygon-on-line overlayAn overlay technique in which polygon features that overlay lines are selected and subsequently preserved in an output layer. operation is the reverse 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 later on preserved in the output layer. For case, given a layer containing the path of a series of telephone poles/wires and a polygon map incorporate metropolis parcels, a polygon-on-line overlay operation would let a land assessor to select those parcels containing overhead telephone wires.

Figure 7.9 Polygon-on-Line Overlay

Finally, the polygon-in-polygon overlayAn overlay technique in which a polygon input and overlay layers are combined to create an output polygon layer with the extent of the overlay. functioning 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 aspect table will contain spatial data and attribute information from both the input and overlay layers (Figure seven.10 "Polygon-in-Polygon Overlay"). For example, you may choose an input polygon layer of soil types with an overlay of agricultural fields inside a given canton. The output polygon layer would contain information on both the location of agricultural fields and soil types throughout the county.

Effigy vii.10 Polygon-in-Polygon Overlay

The overlay operations discussed previously presume that the user desires the overlain layers to be combined. This is not e'er the example. Overlay methods can be more complex than that and therefore utilise the basic Boolean operators: AND, OR, and XOR (see Section 6.1.2 "Measures of Central Trend"). Depending on which operator(s) are utilized, the overlay method employed volition result in an intersection, matrimony, symmetrical deviation, or identity.

Specifically, the spousal relationshipAn overlay method that preserves all features, attribute data, and spatial extents from an input layer. 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 (part (a) of Figure 7.11 "Vector Overlay Methods "). This overlay method is based on the polygon-in-polygon functioning described in Department 7.one.one "Buffering".

Alternatively, the intersectionAn overlay method that contains common features and attributes from both the input and overlay layers. overlay method employs the AND operator. An intersection requires a polygon overlay, simply can take 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 (office (b) of Effigy 7.xi "Vector Overlay Methods ").

The symmetrical differenceAn overlay method that contains those areas common to only one of the feature datasets. overlay method employs the XOR operator, which results in the contrary output equally an intersection. This method requires both input layers to exist polygons. The output polygon layer produced by the symmetrical difference method represents those areas common to simply ane of the feature datasets (part (c) of Figure seven.11 "Vector Overlay Methods ").

In addition to these simple operations, the identityAn overlay method that creates an output layer with the spatial extent of the input layer but includes aspect information from an overlay. (also referred to as "minus") overlay method creates an output layer with the spatial extent of the input layer (part (d) of Figure 7.11 "Vector Overlay Methods ") but includes attribute data from the overlay (referred to equally the "identity" layer, in this example). The input layer can exist points, lines, or polygons. The identity layer must exist a polygon dataset.

Effigy seven.11 Vector Overlay Methods

Other Multilayer Geoprocessing Options

In addition to the aforementioned vector overlay methods, other common multiple layer geoprocessing options are available to the user. These included the clip, erase, and separate tools. The pruneA geoprocessing operation that extracts those features from an input point, line, or polygon layer that falls within the spatial extent of a clip layer. geoprocessing operation is used to extract those features from an input indicate, line, or polygon layer that falls within the spatial extent of the clip layer (function (eastward) of Effigy vii.xi "Vector Overlay Methods "). Post-obit the clip, all attributes from the preserved portion of the input layer are included in the output. If any features are selected during this process, but those selected features within the prune boundary will be included in the output. For example, the clip tool could be used to prune the extent of a river floodplain by the extent of a county purlieus. This would provide county managers with insight into which portions of the floodplain they are responsible to maintain. This is similar to the intersect overlay method; however, the aspect data associated with the clip layer is not carried into the output layer following the overlay.

The eraseA geoprocessing operation that preserves only those areas outside the extent of an erase layer. geoprocessing operation is substantially the opposite of a clip. Whereas the clip tool preserves areas inside an input layer, the erase tool preserves only those areas outside the extent of the analogous erase layer (office (f) of Figure 7.11 "Vector Overlay Methods "). While the input layer can be a bespeak, line, or polygon dataset, the erase layer must exist a polygon dataset. Continuing with our clip example, county managers could and then utilise the erase tool to erase the areas of private ownership within the county floodplain area. Officials could then focus specifically on public reaches of the countywide floodplain for their upkeep and maintenance responsibilities.

The separateA geoprocessing operation that divides an input layer into two or more layers based on a divide layer. geoprocessing functioning is used to divide an input layer into 2 or more layers based on a split up layer (office (g) of Figure seven.11 "Vector Overlay Methods "). The split layer must be a polygon, while the input layers can be betoken, line, or polygon. For example, a homeowner's clan may choose to split upward a countywide soil series map by parcel boundaries then each homeowner has a specific soil map for their own package.

Spatial Join

A spatial join is a hybrid between an attribute functioning and a vector overlay performance. Like the "join" attribute operation described in Department v.ii.two "Joins and Relates", a spatial join results in the combination of 2 feature dataset tables by a common attribute field. Unlike the attribute operation, a spatial join determines which fields from a source layer'due south attribute table are appended to the destination layer'due south attribute table based on the relative locations of selected features. This relationship is explicitly based on the property of proximity or containment between the source and destination layers, rather than the primary or secondary keys. The proximity option is used when the source layer is a point or line characteristic dataset, while the containment option is used when the source layer is a polygon characteristic dataset.

When employing the proximity (or "nearest") option, a record for each feature in the source layer'due south attribute table is appended to the closest given feature in the destination layer's attribute table. The proximity option volition typically add a numerical field to the destination layer attribute table, called "Altitude," within which the measured distance between the source and destination characteristic is placed. For example, suppose a city agency had a signal dataset showing all known polluters in town and a line dataset of all the river segments within the municipal boundary. This agency could and so perform a proximity-based spatial join to determine the nearest river segment that would most likely exist affected by each polluter.

When using the containment (or "inside") pick, a record for each feature in the polygon source layer's attribute table is appended to the record in the destination layer'south attribute table that it contains. If a destination layer feature (point, line, or polygon) is not completely contained within a source polygon, no value will be appended. For instance, suppose a pool cleaning concern wanted to hone its marketing services by providing flyers just to homes that endemic a puddle. They could obtain a signal dataset containing the location of every pool in the county and a polygon packet map for that same area. That business concern could and so conduct a spatial join to append the parcel data to the pool locales. This would provide them with data on the each land parcel that contained a pool and they could afterwards ship their mailers only to those homes.

Overlay Errors

Although overlays are one of the most important tools in a GIS annotator's toolbox, there are some issues that can arise when using this methodology. In detail, sliversA narrow gap formed when the shared purlieus of ii polygons exercise not meet exactly. are a common error produced when two slightly misaligned vector layers are overlain (Figure 7.12 "Slivers"). This misalignment tin come up from several sources including digitization errors, interpretation errors, or source map errors (Chang 2008).Chang, K. 2008. Introduction to Geographic Information Systems. New York: McGraw-Hill. For case, most vegetation and soil maps are created from field survey data, satellite images, and aerial photography. While you can imagine that the boundaries of soils and vegetation frequently coincide, the fact that they were almost likely created by unlike researchers at unlike times suggests that their boundaries volition not perfectly overlap. To ameliorate this problem, GIS software incorporates a cluster toleranceA geoprocessing setting that forces nearby vertices to be snapped together if they fall within a user-specified altitude. selection that forces nearby lines to be snapped together if they autumn within a user-specified distance. Care must be taken when assigning cluster tolerance. Too strict a setting will non snap shared boundaries, while too lenient a setting will snap unintended, neighboring boundaries together (Wang and Donaghy 1995).Wang, F., and P. Donaghy. 1995. "A Written report of the Impact of Automated Editing on Polygon Overlay Analysis Accuracy." Computers and Geosciences 21: 1177–85.

Figure 7.12 Slivers

A second potential source of error associated with the overlay procedure is error propagation. Mistake propagationWhen inaccuracies are nowadays in the original input and overlay layers and are carried through to an output layer. arises when inaccuracies are nowadays in the original input and overlay layers and are propagated through to the output layer (MacDougall 1975).MacDougall, Eastward. 1975. "The Accuracy of Map Overlays." Mural Planning 2: 23–30. These errors tin be related to positional inaccuracies of the points, lines, or polygons. Alternatively, they tin arise from attribute errors in the original data table(due south). Regardless of the source, 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.

Key Takeaways

• Overlay processes place 2 or more thematic maps on top of one another to form a new map.
• Overlay operations available for use with vector data include the betoken-in-polygon, polygon-on-point, line-on-line, line-in-polygon, polygon-on-line, and polygon-in-polygon models.
• Spousal relationship, intersection, symmetrical difference, and identity are common operations used to combine information from various overlain datasets.

Exercises

1. From your own field of study, depict three theoretical data layers that could be overlain to create a new, output map that answers a complex spatial question such as, "Where is the best identify to put a mall?"
2. Go online and observe the vector datasets related to the question you just proposed.

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Source: https://saylordotorg.github.io/text_essentials-of-geographic-information-systems/s11-02-multiple-layer-analysis.html

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