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Coordinate Systems

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What Is a Coordinate Reference System?

Learn what a coordinate reference system is, how it gives coordinates geographic meaning, and how geographic and projected CRSs differ.

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Geographic vs Projected Coordinate Systems

Learn how geographic and projected coordinate reference systems represent location differently, why projections introduce distortion, and which type is appropriate for mapping, exchange, and spatial analysis.

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What Is an EPSG Code?

Learn what an EPSG code identifies, why codes such as EPSG:4326 and EPSG:3857 matter in GIS, and what the number does—and does not—tell you about a coordinate reference system.

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Why Is My GIS Data Appearing in the Wrong Place?

Learn why GIS layers appear in the wrong location, how to distinguish CRS and coordinate-order problems from bad source data, and what to check before changing anything.

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Assigning a CRS vs Reprojecting Data

Learn the difference between assigning a coordinate reference system and reprojecting data, why confusing them can move a layer to the wrong place, and which operation to use.

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EPSG:4326 vs EPSG:3857: WGS 84 and Web Mercator Explained

Learn how EPSG:4326 and EPSG:3857 represent location differently, why web maps commonly use both, and which CRS is appropriate for storage, display, and spatial measurement.

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