By: Eboni Brown & Lauren Greenspan
This tutorial will walk you through creating geographic maps, Histograms, and TreeMaps. These maps will help us visualize data about trees, such as their health, species, or location. We will be using data from iNaturalist and the visualization app tableau public, an easy-to-learn software for data organization and visualization.
Step 0: Preliminaries
- Download Tableau Public from https://public.tableau.com/s/
You will have to type in an email then the file will start to download. Open the TableauPublic file which ends with .dmg in your downloads. Click to open and continue through all the steps to install Tableau Public onto you computer.
- Download the tree dataset from github at https://github.com/TreeMama/Western_Redcedar_iNat. Click the green “code” button and choose “download zip” from the dropdown menu. Two datasets will be downloaded as .csv files, you will be using “classified_trees”.
- Open Tableau Public and upload the dataset. Under the blue “connect” bar, click “text file” and navigate to “classified_trees.csv”. A table with a summary of the data should appear.
Step 1: Mapping Some Trees
It’s time to make some graphics from our uploaded data! First, we’ll make a map of the location of the trees based on their longitude and latitude.
- Click “sheet 1” to move to the worksheet area.
The worksheet area has a “tables” column on the left with headings summarizing the information contained in your data.
In this tutorial, we’re going to be working with the following three data categories .
- Grab the longitude title and drag it to the rectangle next to the word “columns”. Grab the latitude title and drag it to the rectangle next to the word “rows”. Click “symbol maps” from the chart options on the right side of the screen (if it’d hidden, click “show me”). You should see a map with dots – one dot for each picture of a tree taken.
- Now we want to sort the dots according to the health of the tree. Drag “tree health” from the tables menu to “color” in the marks bar. A legend should pop up on the screen. Bonus: How do the dots on the map change, and why? Feel free to play around with the colors and styles of the dots.
- Bonus: Using filters. Drag “Tree Health” to the “filters” box, and click on one (or more) of the options. What changed on your map? What do you think “filters” do?
- Save your work. Click the disk icon to save the visualization to your Tableau dashboard.
Step 2: Histograms
We’d also like to know how many trees in our data are healthy, unhealthy, or dead. We can do this by creating a histogram, which counts the total number of trees in each “Tree Health” category and displays it as a bar graph.
- Open a new worksheet.
- Drag and drop tree health to the columns and also drag and drop tree health to the rows.
- Place the cursor on the right side of the “tree health” bubble. Click the arrow and select “measure” and then “count” from the drop-down menu.
- Choose “horizontal bars” from the chart options. Bonus Question: How many trees from the data are brown? Given the data, is a tree more likely to be healthy or sick? Play around with the colors and text, and don’t forget to save your work!
- Bonus Questions: Add a filter for “Common Name” and play around with the options. What do you notice?
Step 3: TreeMaps
We are now going to make a visualization that shows the relative size of each category in one image. This is called a TreeMap, and it is useful for summarizing data graphically.
- Add a new worksheet.
- Drag and drop tree health to both the columns and the rows.
- Place the cursor on the right side of the “tree health” bubble. Click the arrow and select “measure” and then “count” from the drop-down menu.
- Choose “Tree Graph” from the chart options.
- To display the number of each category on the graph, click “label” and add “<CNT(Tree Health)>” under “<Tree Health>”.
- Bonus Question: What else is in the “Marks” bar? How are the options for color, size, and label reflected in your graph?
- Bonus Question: How does this graph help you understand the data? Play around with the colors and text, and don’t forget to save your work!
Step 4 (Optional): Species Guess TreeMap
Now that you have the hang of tableau, try it out on some different categories of data. Create a TreeMap of “Species Guess”, which gives a list of the types of trees in your data, according to the people who took the pictures. You should see something that looks like this:
- How many types of trees are there?
- Which is the most common?
- Sometimes, people make mistakes in spelling, or mis-remember the name of a tree. This can lead to mis-categorizations of your data! Look at the category names and see if you can spot any errors. How many types of trees do you think there really are? Which is the most common?
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