Learn These Essential Geoprocessing Tools
So you want to geoprocess like a GIS guru, do you? Well, these 7 geoprocessing tools always top the chart in the GIS guru’s hit list. They’re our bread and butter.
Which geoprocessing tools do we use most in GIS software like ArcGIS and QGIS? For newbies in GIS, these 7 GIS processing tools we recommend you learn like the back of your hand.
Ready to get started?
1 The Buffer Tool
Buffers are proximity functions. When you use this geoprocessing tool, it creates a polygon at a set distance surrounding the features.
For example, a buffer is a polygon or collection of cells that are within a specified proximity of a set of features.
Buffers can have fixed and variable distances. In addition, they can be set to geodesic which accounts for the curvature of the Earth.
Buffer Example Chernobyl Exclusion Zone
Chernobyl is the worst nuclear disaster in human history. In a short period of time, it released hundreds of times more radiation than Hiroshima.
Also, it is one of only two classified as a level 7 event (the maximum classification). Surrounding vegetation absorbed radioactive isotopes and died within a week of the blast.
As a result of the deadly toxins released in the atmosphere, safety crew declared a 2600 square kilometer buffer around the nuclear power plant. To this day, this buffer zone is still in effect and it’s called the Chernobyl exclusion zone.
30 years later, the trees remain reddish-brown. There is an estimated 9000 to 93,000 deaths across Europe. And the exclusion zone is still in effect.
The point of the story is that if ArcGIS was around at the time, they could’ve ran the buffer geoprocessing tool. Since the blast, satellites like SPOT have been monitoring the Chernobyl exclsuion zone because of its restrictions.
2 The Clip Tool
The clip tool is an overlay function that cuts out an input layer with the extent of a defined feature boundary. The result of this tool is a new clipped output layer.
If you can picture a cookie cutter, this is like using the clip tool. And carving out vectors and rasters is one of the most common operations in GIS.
In order to clip data, you need points, lines or polygons as input and a polygon as the clipping extent. The preserved data is the result of a clip.
Clip Example Carving out Florida
Florida’s nickname is the sunshine state. You can even find the Sunshine State on their license plate. But how much sunshine does Florida really receive?
It turns out that global horizontal irradiance (GHI) is a good measure of incoming solar radiation. So if you wanted to install a solar panel, GHI is the recommended data set.
If you clip GHI to the Florida state boundary, you can really find how much sunshine Florida really gets. When we clip GHI, we can add it to a map of even summarize the average GHI values.
3 The Merge Tool
What do you do when you have hundreds of data sets, and you want them in a single data set?
You run the Merge Tool .
The merge geoprocessing tool combines data sets that are the same data type (points, lines or polygons). When you run the merge tool, the resulting data will be merged into one.
How is the Merge Tool Used in GIS?
- Add the features to be combined. Make sure they are the same data type.
- Run the tool. Voila, you have all the features in a single file.
Merge Tool Example: A Supermarket Merger
In the United States, two grocery store giants plan to merge a total of 6,500 stores.
We have two existing data sets – Ahold NV and Delhaize Group grocery stores.
The merger between the two grocery stores into one company – Ahold Delhaize – means all grocery stores will be combined into a single data set.
How would you combine data sets?
You can run the merge tool!
When you combine grocery stores (points) from both companies, they all end up in a final data set.
4 The Dissolve Tool
The Dissolve Tool unifies boundaries based on common attribute values.
How does the Dissolve Tool work in GIS?
The Dissolve Tool merges neighboring boundaries based on common attribute values.
An example of using the Dissolve Tool is when you dissolve countries to continents. In order to do this, you would need an attribute in each country record. For each country, there must be a continent field indicating the continent it’s in.
Dissolve Tool Example: Unify West and East or Dissolve Countries to Continents
What do Germany, Yemen, Tanzania and Vietnam all share in common?
They are all examples of two countries dissolving their borders and unifying to form one.
West Germany + East Germany = Germany
North Vietnam + South Vietnam = Vietnam
Country unification is a rare event. But dissolving boundaries in GIS is not.
The dissolve geoprocessing tool erases borders and unifies them into one. When each country has its continent name in the attribute table, you can run the dissolve tool to unify borders into continents.
5 The Intersect Tool
The Intersect Tool is very similar to the clip tool because the the extents of input features defines the output.
The only exception is that it preserves attributes from all the data sets that overlap each other in the output.
How does the Intersect Tool work in GIS?
- Add multiple inputs. The tool accepts different data types (points, lines and polygons).
- When features overlap each other, they will be in the output.
The Intersect Tool preserves the attribute values in both input layers.
Tip of the Day: Run the Intersect Tool on a single feature and you can find overlaps.
Intersect Tool Example: Generating Pivot Tables with Ease
The city councilor asked the GIS analyst: “How many apartments, condos and houses do we have in precinct A, B and C? Create a pivot table for me.”
Instead of running a clip, it would be helpful to run an intersect. Why? Because we preserve attributes from both input data sets. You need the building type from the dwellings layer. You need the precinct ID from the residential layer.
Here’s how to do it:
- Add the dwellings and residential layers to the Intersect Tool input.
- Run the Intersect tool
The output will have all the points that overlap for each precinct. Most importantly, it will keep the dwelling type AND precinct ID.
Select all the rows. Ctrl-C in ArcGIS. Ctrl-V in Excel. Select all. Insert pivot table.
An easier solution: Run the Tabulate Intersection Tool in ArcGIS.
6 The Union Tool
Some say the Union tool should come with a bottle of antacid. The union tool gets a bad reputation because it creates a lot of features.
After running this geoprocessing tool, it does get a bit messy. But it’s really not so bad.
The Union tool spatially combines two data layers. It preserves features from both layers at the same extents.
How does the Union Tool work in GIS?
- Add features you want to union
- Run the tool. It generates more records, especially when there are more overlaps.
Union Example: Basic Shapes
Here’s a simple example of the Union Tool:
We have an overlapping circle and square. The circle is a single record. The square is a single record.
When you run a union on these two features, it produces 3 records – the original circle, the original square and the overlapping portion.
Unions have been especially useful in animal suitability applications because you can understand where different habitat types overlap.
7 The Erase (Difference) Tool
I like the erase tool. It’s always been helpful in erasing things!
The input layer is what will be erased. The erase feature determines what to erase.
Simple as that.
How does the Erase Tool work in GIS?
- Add features you want to erase
- Select the features that you want to erase with.
The result is a new feature with the erase feature extent removed.
Erase Tool Example: Wildfires Tearing Through Forests Calls for the Erase Tool
Humans start 90% of wildfires. Lightning strikes the Earth 100,000 times a day. 10 to 20% of these lightning strikes can cause a forest fires.
No matter how you slice it, forest fires are happening all times somewhere on Earth.
Ecologists need to understand how much suitable habitat exists on the landscape.
When a forest fire tears through a forest:
You can run the erase tool because these forest stands no longer exist. They are no longer suitable habitat for certain species.
Erase those areas with the wildfire polygons and BOOM, you have an updated habitat extent.
You’re Ready to Take the Geoprocessing Training Wheels Off
We’ve sifted through the big 7 geoprocessing tools.
These are so common that ArcGIS and QGIS have added them to drop-down menus for easy access.
When you learn these 7 geoprocessing tools, you develop a good baseline of GIS skills.
On top of that, you are one step closer to becoming a GIS guru.
Comments below. Let me know.
Actually, there are thousands of geoprocessing tools. In our GIS analysis section, it’s a good place to start. Also, you check out Esri’s Spatial Analysis Map for more real world examples of GIS Processing.