Semrush's Google US database analyzes the first 100 organic results for each keyword to gather data for our Domain Analytics and Keyword Analytics reports.
We gather these keywords by looking for the keywords that have the most search volume on Google. Basically, the more popular a keyword is, the more likely we will carry it in our database.
Although there are billions of keywords covered in our system, sometimes keywords will be omitted due to low search volume to make room for more popular/relevant keywords. In order to determine if we cover the keyword you are looking for, simply search the keyword in the main search bar in Semrush and you will immediately be shown all the data we have in our system for your keyword in a Keyword Overview report.
This is how we gather information on what keywords domains are ranking for on the national level in our Domain Analytics and Keyword Analytics. In tools like Position Tracking and Traffic Analytics, data gathering is different.