Where does spatial data come from?

Basic example (data about places, probably counties)

Suppose you wanted to make a map of the counties of Ohio. There are already existing maps of that, but what if you wanted to include data like income levels, housing prices, average age, religious adherence, or anything else you can think of? Where would you find a basic map that you can add data to build the map you wanted?

Where to find shapefiles

Often times, you can find a shapefile just by searching online (i.e. googling) for it (for the above example, searching for "Ohio counties shapefile" will likely get you what you want). But if you can't find what you want easily with a search, or you want to make sure that you have an authoritative map, there are some examples of places to look listed below.

US Census Maps and Data (https://www.census.gov/geographies/mapping-files/time-series/geo/tiger-line-file.html)
IPUMS NHGIS - also houses census type data that can be easily joined (https://www.nhgis.org/)
CAGIS – has some more specific data from Hamilton County (https://data-cagisportal.opendata.arcgis.com/)

It is also possible to create your own. This is more of a last resort but can unavoidable if you are mapping something very new or very old. Old stuff would likely be created referencing a map from/of the period.

About Joins

Sometimes you have the spatial data and you want to look at characteristics of the spatial units. If you do not have the characteristics already in the data set, you might be able to connect a different data set containing this information by joining the two together. In most GIS software, this is called a join. A Join means to connect data sets using a common attribute or characteristic.

Here is an example:

You have census tract data and you want to look at a characteristic such as population. You can connect them using the FIPS code which could be a common attribute of both.

Data can be added to spatial data, allowing you to view where that data actually is.
To do this, you will need a field that is the same in the data table and the spatial layer. This could be names, or abbreviations, but generally the best way in the US is to use the FIPS code
FIPS codes are numerical codes for every state, county, census tract, etc., with a set of numbers for each level that are concatenated for the full identifier.
As of May 2023, FIPS codes are now officially called INCITS codes, but will likely still be called FIPS codes in many older data sets.

The image shows the numbers in a FIPS code with state in brown and at the left side of the number, then county in blue, tract in red and block in yellow.