Define the question first
“Monthly rainfall by station in one region from 2015 to 2025” is a better dataset brief than “weather CSV.” It tells you what a row should represent, which dates matter, and which locations belong in the result. Write that brief before opening a spreadsheet.
A CSV can hold rows and columns without telling you whether a field is an identifier, a measurement, or a date. W3C's CSV on the Web primer describes this gap and the role of accompanying metadata. Finding a downloadable file is therefore only the first part of finding usable data. W3C CSV on the Web primer.
Search for the data and its source
Try a focused query such as monthly rainfall filetype:csv, then add the place or measurement your project requires. FindFiles.net's search by file type guide explains format-based discovery. These examples demonstrate the query syntax; the presence and completeness of results depend on the index.
When you recognize a publisher, visit its dataset catalog as well. Data.gov explains that it is a metadata catalog: agencies maintain the actual data, and the catalog links to their distributions. A file can therefore be hosted somewhere other than the catalog's own domain. Data.gov user guide.
Use site: only when you know the relevant file host. If a CSV search finds nothing, broaden to the dataset title without a format restriction on the publisher's own site. You may find an export button, an API, or a ZIP containing several files. Avoid treating a missing search result as evidence that the underlying data does not exist.
Recover the missing context
For each candidate, create a short source note. Record the publisher, geographic scope, observation period, update policy, and link to the data dictionary. Locate the reuse terms on the dataset record rather than inferring them from public access. Data.gov's Access & Use section displays license information when the publisher supplies it.
Keep three dates separate: when the events were observed, when the data changed, and when a catalog last checked its metadata. The DCAT-US dataset specification explicitly distinguishes a dataset's modification date from a metadata-only change. That distinction helps you avoid describing old observations as new data. DCAT-US dataset metadata.
If the documentation leaves a central question unanswered, write it down. For rainfall, that might be the measurement unit or treatment of a missing day. A larger download cannot answer a question the publisher has not documented.
Inspect a small sample
Preview the header and a few records before importing the entire file. Check the delimiter, character encoding, and whether quotation marks contain separators inside a value. Compare the resulting columns with the data dictionary.
Then test one record you can interpret by hand. Does a station identifier retain its leading zeros? Is the date unambiguous? Does a blank cell mean no measurement, or does the publisher define a different meaning? W3C's metadata approach covers datatypes, formats, and validation precisely because the raw CSV cannot carry all these constraints itself.
Use the application's import preview to set identifier columns to text where needed. After importing, compare those first records with the original file. This small check gives you a concrete chance to catch an unwanted conversion before charts or joins hide it.
Keep the version reproducible
Save the untouched download separately from your cleaned working copy. Record its source URL, download date, and version identifier. When the repository provides a persistent identifier for a particular release, keep that identifier with the file.
Zenodo offers a useful example: published record files are immutable, while a new dataset version is a separate record with its own identifier. Referencing the specific version allows another reader to retrieve the same files. Do not assume every publisher follows that policy; check the repository's documentation. Zenodo record and version lifecycle.
Decide whether the file is usable
Your acceptance note should answer four questions: who published this, what does each row mean, does it cover my question, and can I retrieve the same version again? Add the applicable reuse terms and any unresolved limitations. If you cannot explain a key column, keep searching for documentation before using it in an analysis.