A download button makes data feel ready to use. Click it, open the file, and the rows are waiting. What is less obvious is how much of the meaning may still be sitting on the page you just closed.
Before sorting or making a chart, spend a few minutes with the description. The aim is to work out what the file can help you answer, and where it might lead you astray.
Start with the question, not the size of the file
A large dataset can be a poor match for a small, specific question. Suppose you want to compare visits to two parks. A file of citywide totals will not tell you which park people used. A count of events held in each park will not tell you how many people attended them.
Write your question in one sentence. Then check whether the file contains the place, period and kind of measurement that sentence requires. This example is hypothetical, but the habit works across many subjects.
Find the publisher and the original page
A search result or catalog entry may point somewhere else for the actual data. Data.gov’s user guide, for example, explains that its catalog holds descriptions and access links while individual publishers maintain the underlying datasets.
Keep the source page as well as the file. A filename alone is a weak record of where something came from. Note who published it, when you accessed it and which version you used, if a version is provided.
Read the dates carefully
The date a page was updated is not necessarily the period the measurements describe. A catalog could be revised today while linking to observations collected several years ago.
Look for the coverage period inside the documentation. If you are comparing two files, check that their time windows line up. An annual total and a monthly total are not directly comparable just because the column headings look similar.
Decode one row before you analyse a thousand
Choose a row and explain it in ordinary language. What does it describe? What are the units? Does a blank mean missing, not applicable or zero? Check the data dictionary or accompanying notes rather than deciding from appearance.
For an imagined park-visits file, a value of 120 might mean visits, unique visitors or a daily average. Those are three different statements. If you cannot explain one row confidently, pause before calculating a total.
Leave yourself a short trail of notes
Record the source link, coverage dates, relevant definitions and anything you still do not understand. Read the published access and reuse terms; do not infer permission from the presence of a download link.
You can then make an informed choice: use the file for your question, narrow the question, or look for a better fit. When you are ready to draw a chart, check what its scale is doing before writing the headline.