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Only data stored in CSV files is suitable for visualization. The only data that can be graphed is where there is a numeric parameter with text fields, or else text fields that it makes sense to summarise with a count.
A maximum of 1000 data points are shown on the graph for performance reasons. This will be taken from the top of the resource, so it's important to understand that the graph you're displaying may be filtered if you are looking at a large data file.