This week, I learned about the making of Choropleth map using ArcGIS in my GIS class taught by Heather-Richards Risetto. Choropleth map shows differences in regions, or in a geographical area in a form of color shading. The color shading is made to convey patterns behind complex statistical data. I love this map honestly because it’s a bit artistic with the color playing and shapes. The visualization reminds me of puzzles!
I have created this map before in my data visualization class with Matt Waite using R studio with packages like ‘devtools’, ‘sf’, ‘ggplot’, ‘colorbrewer’, and ‘dplyr’ and a small portion of coding.
However, in this GIS class, I don’t need to use coding commands as I only use ArcGIS to make maps by joining and inserting data to ArcGIS.
So, what steps should be considered when creating Choropleth map (joining tabular data with the spatial data)? First, you need to make sure you have two forms of files: CSV and SHP.
CSV file is like a spreadsheet of all of your statistical data, or data which contains information or numbers that you want to insert as points, lines or polygons in your map. If you have data from the government or any kind of organizations, please, please, please, ask them to send it in a form of a spreadsheet. It will be easier for you to clean the data and use it for the sake of this mapping creation.
Second, make sure you also have the shp file. Okay, what is a shp file? A shp or a shapefile is basically a vector data which has information about the attributes of a geographical area including location and shape. It usually has the longitude and latitude information as it will be the geographical template or the first layer for your statistical data. Still confused? Okay, I am gonna show you the physical forms below.
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this is a physical form of a shp file in QGIS (Ive learned QGIS with Matt, not in the GIS class) -
A shp file can be uploaded into your workspace in QGIS or ArcGIS. Look at the information of layers name in the left side of the picture – fires1apple is my shapefile. -
This is what it looks as a file before you upload it.
Third, you need to have similar features or attributes to merge those two files. What kind of similar features or attributes? We merge tabular data and vector data with a field called GISJOIN or if you have latitude and longitude info in both of your data that shows the same location (or minimum having addresses will be sufficient to be merged with the vector data), it would be great. ArcGIS will automatically combine these two data (tabular and vector) into one. I remember Matt telling during the consultation session,” making a map is easy if you can find similarities among two data.”
And what are the steps to combine the data? It will be a little bit longer to explain here because you need to do several steps like intersect, join, add new field, field calculator, calculate geometry, and so on (Don’t get scared! lol).
But, I am gonna update you next week after completing my interviews and transcribing all of my interviews in Palu (since I will have a routine of doing one-on-one consultation with Matt every Monday). So, I will share with you first the end result of my lab assignment to merge data from the US Census Tract with the vector data (shp file). Here’s the final result:
