How to Quote a Topo50 Map Reference
New Zealand's Topo50 maps carry a sheet code — two letters and two digits, like BP34 for Masterton — and the standard way to quote a position is that sheet code followed by a six-figure grid reference. The letters count bands southward down the country, the digits count columns eastward, and the six figures work exactly like grid references everywhere: easting first, then northing. Prefer to skip sheets altogether? Full NZTM coordinates are unique nationwide — our converter reads yours from GPS in one tap.
How sheet codes work
The Topo50 series slices New Zealand into a lettered-and-numbered chessboard: the two letters name a horizontal band, stepping alphabetically as you move south down the country, and the two digits name a column, increasing as you move east. Real anchors make the pattern obvious: AW26 is Hokianga Harbour in Northland, BG36 is Taupō in the central North Island, BP34 is Masterton in the lower North Island — letters marching south, numbers tracking east. Neighbouring sheets differ by one letter-step or one digit, which is how you name the next map over without a catalogue.
Sheet + six figures — why the sheet matters
A six-figure reference names a 100 m square within a 100 km grid block — and the same six figures repeat in every block up and down the country. The sheet code is what pins them to one place, which is why the New Zealand convention is to say it first: "BP34, eight-nine-one, zero-one-three". On the radio or phone that ordering also fails safe — if the figures get garbled, the listener at least knows which map to spread out. It's the same everywhere-first logic as square letters in Britain and Ireland, wearing a Kiwi uniform.
Or skip the sheet: full NZTM
Because the whole country lives in a single NZTM zone, the full coordinates — a 7-digit easting and 7-digit northing — are unique nationwide with no sheet required. That's the format DOC's systems, beacon registrations and GIS work take, and it's what our NZTM converter gives you in one tap, along with the six-figure form for radio use. A sensible habit for the backcountry: note both before you lose signal. The page keeps working offline once loaded, precisely for that moment.
The old NZMS260 series — don't mix eras
Before Topo50 arrived in 2009, the NZMS260 series ruled — different sheet codes (a letter-number style like S26), a different projection (NZMG) and the older NZGD1949 datum, offset from today's maps by roughly 200 m at the datum level. References from old guidebooks, hut logs and route descriptions written for NZMS260 don't transfer digit-for-digit onto Topo50 sheets. If you're working from vintage beta, convert properly (LINZ publishes the tools) or re-derive the position from the map — never assume the numbers survived the changeover.
Step by step
- Read the sheet code off the map's corner — two letters + two digits, like BP34.
- Find the vertical grid line just left (west) of your point and read its two large printed digits — the start of your easting.
- Estimate tenths from that line east to your point for the third figure.
- Do the same with the horizontal line below your point for the northing: two digits, plus estimated tenths.
- Quote it sheet first: "BP34 891 013" — sheet code, easting trio, northing trio, digits read out one at a time.