Merging Layers in ArcGIS

Esri is a company specialized in Geographic Information System tools. ArcGIS, ArcMap are two of the most commonly used and powerful tools among all the GIS tools provided. As more and more data in incorporating geo-coded information to provide details of certain events, GIS has become more and more popular among data analysts and business intelligent.

ArcGIS and ArcMap are available for download on arcgis.com. The price for these tools are very expensive. If you belong to an educational institution, you may want to check with the related departments to see if such tools are provided free of charge within your institution. For businesses, contacting Esri getting a contract might be a better idea based on the scale of business. Here I am using ArcMap under free trial. You can sign up to use the software free of charge for a certain period of time.

An example of ArcMap interface looks like below:

arcmap_intro

On the left hand side, the window displays the file and layers opened. On the right hand side, where the white blank space is displayed, is the mapping console where maps will be displayed. The top bars, like most other programs, have options and tool bars for users to explore.

When you open/create/save a file in ArcMap, in the actual folder you have designated, there are usually multiple files with different extensions as below:

arcmap_file

.shp is the file actually opened in the ArcMap. It is called shape file. You can drag it into ArcMap and the program will process this type of file automatically.

.dbf file is the database file. You can open an excel and have this file opened as a common separated value file (csv) file. Please be noted the limitation of excel might apply to the data file.

There might be more files that the ones shown above, like xml file and other file types. Noted although usually .shp and .dbf are the most commonly used, when moving/copying the files, all the files, including all extensions, need to be moved together in order to process appropriately.

Adding data in ArcMap is straightforward. Find the icon in the toolbar and select files you want to include. Make sure Longitude and Latitude are in different columns with standard format. If the original file is in excel, make sure these two fields are in number format.

After adding the data into the ArcMap, the file will be displayed in the left hand side Table of Contents section. Right click the file and select XY data to plot it as a layer. Select the corresponding column in the original file with coordination system.

After that, the map should be able to show you the visualization that looks like this:

arcmap_events.JPG

The file created correspondingly is called events file. This file is the visualization of what each geographic location of every record in the original data file. To have more done with the file, we need you convert this event file into a layer in the ArcMap. Right click on the event file, and select Data–> Export Data.

arcmap_exportlayer

Select the folder location you want to save the layer file (the marked area) and make sure you have select the layer’s source data in the coordinate system option. The Table of Contents window should have something similar as below:

arcmap_pointlayer

The highlighted file with green dots underneath is called point data/layer. Where on the map, each point represents one record in the original data file. In contrast, there is another type of data called shapefile which represents a whole area in the map. An example is shown below:

arcmap_ieshpfile

This is an example of California state by counties. Such files are available at some public sector websites. Select the file with extension .shp and drag into ArcMap.

Now that we’ve got both point layer and shape layer, how do we know if certain event is occurring within certain area? In that case, we need to merge two layers.

The merging layers operation in ArcMap is directional. When you want to aggregate data, i.e. how many events have occurred in certain area, you are merging the shape layer to the point layer. In contrast, if you are interesting knowing the detailed information of each event, i.e. what is the area location information of each event, you are merging the point layer to the shape layer.

In ArcMap, such difference is determined by which file you right click. For the aggregate data option, right click the shape layer and select Join.

arcmap_agg

After selecting the desired method of aggregating, you will have another file listed as an output on the left hand side. Select it and open the attribute table will give you a data file in csv-similar format and you can manipulate or process it later easily with other data tools.

Having point-detailed data is a reverse operation. Right click on the point layer and select Join.

arcmap_detail

Notice the difference between the highlighted part for two methods. You have 2 options in the detailed point layer for falls inside and closest to it. You can choose based on your need.

For both methods, there will be several files created with various extensions we have discussed previously created in your designated folder location. I suggest for each file you create a unique folder to store them. Because the names automatically generated by ArcMap are identical to each other, for better sorting option, it makes sense to store them into different folders.

 

 

 

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