Define Your Data Grain Before Picking a Chart, Analysts Warned

A data modelling guide published on DEV Community argues that the most common error in business reporting is not poor chart design but mismatched data grain — the unit that each row in a dataset represents. Mixing invoice-level, line-level, payment, and financial-summary data in a single table causes totals to multiply and filters to answer the wrong question. The article illustrates the risk with a concrete example: joining a £1,000 invoice total across five line items and summing the result incorrectly yields £5,000. Analysts are advised to state the reporting question in plain language first, then select the appropriate grain — such as one row per invoice, per product line, or per payment — before building any visualisation. The guide also recommends keeping separate fact tables for each natural grain and documenting non-additive measures to ensure dashboards remain accurate when data is refreshed.