Can Two Datasets of Different Scales Be Overlay in Arcgis?
- Overlay methods
- Overlay tools
One of the most bones questions asked of a GIS is "What's on height of what?" For example:
- What land use is on top of what soil blazon?
- What parcels are within the 100-year floodplain? ("Within" is just another manner of saying "on top of.")
- What roads are within what counties?
- What wells are within abandoned military bases?
To answer such questions before the days of GIS, cartographers would create maps on articulate plastic sheets and overlay these sheets on a light table to create a new map of the overlaid information. Because overlay yields such valuable information, it was paramount to the evolution of GIS.
An overlay operation is much more than than a simple merging of line piece of work; all the attributes of the features taking part in the overlay are carried through, as shown in the example below, where parcels (polygons) and flood zones (polygons) are overlaid (using the Spousal relationship tool) to create a new polygon dataset. The parcels are split up where they are crossed by the inundation zone purlieus, and new polygons created. The FID_flood value indicates whether polygons are outside (-1) or inside the inundation zone, and all polygons retain their original land-utilize category values.
The total area of each land-use blazon in the flood zone tin be calculated past selecting all polygons inside the flood zone (using the Select Layer By Attribute tool, for example) and summarizing the surface area by land-apply type (using the Frequency tool). Following is a chart illustrating the upshot of this calculation.
Similarly, yous'd overlay watershed boundaries with a vegetation layer to calculate the corporeality of each vegetation blazon in each watershed.
In the illustration beneath, logging roads (lines) and vegetation types (polygons) are overlaid to create a new line characteristic class. The lines take been split where they were intersected past polygons, and each line feature has been assigned the attributes of both original layers. The lines are shown symbolized by the vegetation blazon associated with each.
You can utilize overlay analysis to combine the characteristics of several datasets into one. You can then find specific locations or areas that have a certain set of attribute values—that is, match the criteria you lot specify. This approach is often used to find locations that are suitable for a item employ or are susceptible to some take chances. For example, you'd overlay layers of vegetation type, slope, attribute, soil moisture, and then on, to find areas susceptible to wildfire.
Below is an example of an overlay of steep slopes, soils, and vegetation. New polygons are created by the intersection of the input polygon boundaries. The resulting polygons have all the attributes of the original polygons.
Overlay assay is often used in conjunction with other types of assay. For example, you might include datasets derived from proximity analysis (such as the Buffer tool) or surface analysis (the Gradient or Attribute tool). Similarly, you'll likely perform additional assay on the results of the overlay, such as extraction to select a subset of features, or generalization (to dissolve polygons, for example). Oftentimes, overlay is one step in an analysis process or model and may occur at diverse points in the procedure.
Overlay methods
In general, at that place are two methods for performing overlay analysis—characteristic overlay (overlaying points, lines, or polygons) and raster overlay. Some types of overlay analysis lend themselves to i or the other of these methods. Overlay analysis to find locations meeting certain criteria is often best done using raster overlay (although you can do it with characteristic information). Of course, this also depends on whether your information is already stored as features or rasters. Information technology may exist worthwhile to catechumen the data from i format to the other to perform the analysis.
Characteristic overlay
The key elements in feature overlay are the input layer, the overlay layer, and the output layer. The overlay function splits features in the input layer where they are overlapped by features in the overlay layer. New areas are created where polygons intersect. If the input layer contains lines, the lines are split where polygons cantankerous them. These new features are stored in the output layer—the original input layer is non modified. The attributes of features in the overlay layer are assigned to the appropriate new features in the output layer, forth with the original attributes from the input layer.
Below is an instance of line-on-polygon overlay. The line is split at the polygon boundaries, and each of the resulting line features has the original line attributes plus the attributes of the polygon it brutal within.
Raster overlay
In raster overlay, each cell of each layer references the aforementioned geographic location. That makes it well suited to combining characteristics for numerous layers into a unmarried layer. Usually, numeric values are assigned to each characteristic, allowing you to mathematically combine the layers and assign a new value to each prison cell in the output layer.
Below is an example of raster overlay by addition. Ii input rasters are added together to create an output raster with the values for each jail cell summed.
This arroyo is oftentimes used to rank attribute values by suitability or risk, then add together them to produce an overall rank for each cell. The various layers can also be assigned a relative importance to create a weighted ranking (the ranks in each layer are multiplied by that layer's weight value before existence summed with the other layers).
Below is an example of raster overlay by improver for suitability modeling. Three raster layers (steep slopes, soils, and vegetation) are ranked for development suitability on a calibration of ane to 7. When the layers are added (bottom), each cell is ranked on a scale of 3 to 21.
Alternatively, you can assign a value to each cell in the output layer based on unique combinations of values from several input layers.
Overlay tools
Vector overlay tools
Feature overlay tools are located in the Analysis toolbox in the Overlay toolset. Conceptually, the tools are similar—they differ by the feature types they allow you to overlay, past whether y'all tin can overlay multiple layers at one fourth dimension, and by which input and overlay features are maintained in the output layer.
| Tool | Binary or multiple overlay | Input data type | Overlay data type | Output |
|---|---|---|---|---|
| Identity | Binary | Whatsoever | Polygon or aforementioned as input | Input features, dissever by overlay features |
| Intersect | Multiple | Any | Northward/A | Only features common to all input layers |
| Symmetrical departure | Binary | Any | Same as input | Features common to either input layer or overlay layer just non both |
| Union | Multiple | Polygon | Due north/A | All input features |
| Update | Binary | Any | Polygon | Input feature geometry replaced past update layer |
The table below shows the results of overlaying an input dataset and an overlay dataset using each tool.
| Input features | Overlay features | Functioning | Effect |
|---|---|---|---|
| | | Identity | |
| | | Intersect | |
| | | Symmetrical difference | |
| | | Spousal relationship | |
| | | Update | |
Raster overlay tools
Raster overlay tools are located in several toolsets in the Spatial Analyst toolbox. Spatial Analyst is an ArcGIS extension that is licensed separately. If your site has a Spatial Analyst license and the Spatial Analyst extension has been installed, you will have admission to the Spatial Annotator toolbox in ArcToolbox.
| Tool | Location | What information technology does |
|---|---|---|
| Zonal Statistics | Zonal toolset | Summarizes values in a raster layer past zones (categories) in another layer—for case, calculate the mean elevation for each vegetation category. |
| Combine | Local toolset | Assigns a value to each cell in the output layer based on unique combinations of values from several input layers. |
| Weighted Overlay | Overlay toolset | Automates the raster overlay process and lets you assign weights to each layer earlier calculation (you tin also specify equal influence to create an unweighted overlay). |
| Weighted Sum | Overlay toolset | Overlays several rasters, multiplying each past their given weight and summing them together. |
Related Topics
- An introduction to the ordinarily used GIS tools
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Source: https://desktop.arcgis.com/en/arcmap/10.3/analyze/commonly-used-tools/overlay-analysis.htm
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