An NZTM coordinate like (1,580,000 , 5,180,000) plotted as WGS84 degrees would place the data at longitude 1,580,000° — a point that doesn't exist on Earth.
This is what happens when you use
set_crs(4326) on NZTM data instead of to_crs(4326).
CRS Explorer
See how projections distort the world and why CRS matters for NZ engineering
1. Scale & View
2. CRS Mode
| Property | WGS84 |
|---|---|
| EPSG Code | 4326 |
| Type | Geographic |
| Units | Degrees (°) |
| Best for | GPS, web maps, data sharing |
.area returns | degrees² (meaningless!) |
.buffer(100) | 100° ≈ 11,000 km radius |
3. Measure Distance
Click two points on the map to measure distance in metres and degrees.
Layers
Guided Questions
In the World View, compare the green Greenland and orange Africa outlines. Estimate how their sizes compare on this map. Now look up their actual areas online (in km²). How much does the map distort them, and why?
Switch to New Brighton view and move your mouse across the map. Watch the coordinate bar at the bottom. What units does WGS84 use? What units does NZTM use? Which CRS would you use to measure a 100m pipe?
Click the Mismatch! button. Read the warning. Explain in your own words: what is the difference between set_crs() and to_crs()? What goes wrong if you use the wrong one?
Use the Measure Distance tool on the NB map. Click two points ~500m apart. Compare the result in metres vs degrees. At latitude 43.5°S, how many metres is 0.001° of longitude?
After the Canterbury earthquakes, the ground moved up to 0.5m vertically and several metres horizontally. What implications does this have for spatial datasets created before 2010? Think about flood models, pipe networks, and property boundaries.