You could buffer the stream to 100 meters and then "Erase" the stream buffer layer from the original grazing area layer. The Erase tool uses one layer to "erase" area from another layer.Ĭase Study: Find Legal Grazing Land (Post Ordinance).Īn example of "Erase" would be to find grazing land near a stream if you were required to restrict grazing to be at least 100 meters from the stream. Notice that the only difference is that the attributes are only maintained for the first layer. Clipping Trails Layer to Streams BufferĬlip is commonly used and is closely related to "Intersect". The Clip Tool only maintains the attributes for the original layer. The Clip tool "clips" one layer with all the features from another. Now the features have been "dissolved" together into larger features. Here we have selected the dissolve tool and the "HUName" field in the attribute table. We can dissolve features together based on an attribute that has the same values for the features to be resolved together, in this case, the Hydrologic Unit (HU) name. An example of this is to combine drainages for each river.Ī layer showing the drainages, or watersheds in an area. This is a proper union.ĭissolving is helpful when removing unneeded information, and typically should be executed prior to applying an area based selection. This tool dissolves features in a layer together, which can be based on a common attribute value or all features together. The Union tool in ArcGIS is not used much but is presented here to prevent confusion with the "Dissolve" tool described below.ĪrcMap's Union Tool does not perform a Union as shown above, for this you need to use "Dissolve" in the next section. The resulting features are the unique areas between the two layers. In other words, it creates the "Union" of two layers, rather than a spatial union as shown above. The Union tool in ArcMap combines the features from one or more layers into a single layer. The image below shows a "true" union as you may have learned in geometry. The result would be the habitat for the mushroom. We could now take a layer that contained features of Klamath Mixed Conifer Forests and another that showed the annual precipitation was over 50 inches and intersect the two. If we know that the species requires requires: The Intersect Tool maintains the attributes for both intersecting features.Ĭase Study: Distribution of a Rare Fungal SpeciesĪn example of using intersection would be if we wanted to find the habitat for a rare species such as the mushroom shown below. The Intersect tool finds the intersection of features between two or more layers. The diagram below illustrates the effect of switching the Input Coverage with the Union Coverage and the resulting User-ID of the segment of the arc that overlaps in the Output Coverage.Below is additional detail on overlay operations in ArcMap with examples. If arcs in the Input Coverage and the Union Coverage overlap, then after running a Union followed by a Build LINE, the User-IDs of the arcs in the Input Coverage will take precedence over the overlap sections. The attribute tables are updated for all three commands. They differ from Union only in the features that remain in the Output Coverage. Two others are similar: Intersect and Identity.
![union arcmap union arcmap](https://desktop.arcgis.com/en/arcmap/10.3/tools/analysis-toolbox/GUID-53BD6811-F2C0-4A3D-89E2-BC545BF6826D-web.gif)
Union is one of several Overlay commands available in the Coverage toolbox. For polygon input coverages Using the JOIN option (default)
![union arcmap union arcmap](https://i.ytimg.com/vi/6TvckNpIhJ0/maxresdefault.jpg)
The following table list the items that are saved in the polygon feature class for the Output Coverage. Items are merged into the output polygon feature class using the old internal number of each polygon. The feature attribute table for the Output Coverage contains items from both the input and Union Coverage attribute tables. The resulting arcs are used to build polygons using a process similar to the Build tool with the POLY option. Arcs of the Input Coverage polygons are split at their intersection with polygons of the Union Coverage. Only polygon coverages can be combined using Union. The Output Coverage contains the combined polygons and attributes of both coverages. The Union tool creates a new coverage by overlaying two polygon coverages.