What should an ArcGIS user do to ensure data layers align correctly when using different projections?

To ensure that data layers align correctly when using different projections, transforming all layers to a single coordinate system before adding them to the map is essential. When different layers are created or projected in various coordinate systems, they are like pieces of a puzzle that won’t fit together unless they are modified to share a common reference frame.

By performing a transformation, you convert each layer into a single coordinate system, facilitating accurate spatial analysis and proper visualization of the data in relation to one another. This process mitigates alignment issues, ensuring that all layers overlay correctly within the map.

While changing the map's projection to match the first layer added may seem like a potential solution, it does not guarantee that all layers will be accurately represented since every layer could still be in a different projection. Similarly, adjusting the layer order in the Table of Contents or using the Project tool on data layers may not resolve alignment issues effectively unless every layer is consistently transformed to the same coordinate system first. Transforming all layers is a more comprehensive and reliable approach to ensure proper alignment of data when using different projections.