Few beginner GIS problems cause as much confusion as coordinate systems. A layer that should sit over a town lands in the ocean, distances come out in degrees instead of metres, or two maps of the same place refuse to line up. Almost always, the cause is a mismatch between WGS84 and a projected system such as UTM. Both systems describe locations on Earth, but they do it in different units and for different purposes. Once you understand what each one is for, most alignment problems become easy to diagnose and fix.

WGS84 is a geographic coordinate system that locates any point by latitude and longitude in degrees. It is the system used by GPS receivers, web maps, and most satellite data downloads, and it works everywhere on Earth with a single set of coordinates. Its weakness is measurement: a degree of longitude is much longer at the equator than near the poles, so distances, areas, and buffers computed directly in degrees are distorted and hard to interpret. WGS84 is excellent for storing and sharing global data and for displaying it on a web map, but it is a poor choice for measuring a field, a road length, or a buffer distance without converting first.

The Universal Transverse Mercator system divides the world into sixty zones, each six degrees of longitude wide, and projects locations inside each zone onto a flat grid measured in metres. Within a zone, distortion is small, so distances and areas are meaningful and easy to work with. The catch is the zone boundary: a project that crosses from one UTM zone into the next needs care, because coordinates in one zone do not compare directly with coordinates in another. For most local projects, choose the UTM zone that contains your study area, work in metres, and note the zone number in your project documentation so the next person can reproduce your measurements.

Misalignment usually happens when software is told the wrong coordinate system for a layer, not when the data itself is wrong. If a UTM layer measured in metres is mistakenly read as degrees, it will appear as a tiny speck near the equator. If a WGS84 layer is read as UTM metres, it may vanish or land far away. The fix in QGIS is to check each layer's properties, confirm its stated system against the data provider's documentation, and reproject with the export or warp tools when a change is genuinely needed, rather than just relabelling the system. Relabelling without reprojecting changes the interpretation of the numbers without changing the numbers themselves, which is how layers end up in the wrong place while looking correct in the layer list.

Store shared and downloaded data in WGS84, which is the common exchange format, and do measurement work in a local projected system such as the UTM zone for your area. In QGIS, set the project coordinate system to the projected system, enable on-the-fly reprojection so layers display together, and check a known landmark after loading each new layer. If distances suddenly look wrong, check the project system before blaming the data. Write the coordinate system used for each output map in its credits or notes, because a map without a stated system is hard for anyone else to reuse with confidence.

Think of WGS84 as the global address and UTM as the local measuring tape. Keep data in WGS84 for sharing, measure in UTM for local work, and verify every new layer against a landmark you recognise. That single habit prevents most of the mysterious misalignments that frustrate new GIS users.