Grid ref­er­ence skills

Trail (UK) - - CONTENTS - Ia■ Mor­ris, via emai● Pau● says

QIf I need to con­vert an eight- or 10-fig­ure grid ref­er­ence to a six­fig­ure ref­er­ence, should I round up or round down the sur­plus dig­its?

You should al­ways round down a grid ref­er­ence. Re­mem­ber, a grid ref­er­ence in­di­cates the bot­tom-left cor­ner of the grid square it ref­er­ences. The area size the grid square rep­re­sents is de­ter­mined by how many fig­ures com­pose the ref­er­ence, so a four-fig­ure grid ref­er­ence in­di­cates a 1km square, a six-fig­ure grid ref­er­ence in­di­cates a 100m square, an eight-fig­ure grid ref­er­ence in­di­cates a 10m square, and a 10-fig­ure grid ref­er­ence in­di­cates a 1m square.

Grid ref­er­ences also al­ways in­clude a two­let­ter de­scrip­tor at the start, in­di­cat­ing the par­tic­u­lar 100km square area of an OS map in which the ref­er­ence lies. These let­ters are marked in blue in the cor­ner of an OS map.

If we have a 10-fig­ure grid ref­er­ence, for ex­am­ple from a satel­lite nav­i­ga­tion de­vice, and we want to round it to a six-fig­ure, al­ways round down the last two least sig­nif­i­cant dig­its from each side to zero. In other words, we ig­nore the last two dig­its on each side. Like­wise, with eight-digit grid ref­er­ences, round down the sin­gle least sig­nif­i­cant digit on each side to zero. So, if you have a 10-fig­ure grid ref­er­ence that reads SK12599

95799, it would be­come SK125957 as a six­fig­ure ref­er­ence.

Even though the lo­ca­tion ref­er­enced is numer­i­cally nearer to the SK126958 grid square in terms of dis­tance on the ground, the lo­ca­tion is still deemed to be in the

SK125957 grid square.

Paul is co-founder of the UNS – a char­ity pro­vid­ing nav­i­ga­tion cour­ses for hill­walk­ers, with all prof­its go­ing back into the hills. Trail read­ers can cur­rently en­joy 10% off the School’s week­end nav­i­ga­tion cour­ses! Sim­ply go to www.ul­ti­mate­nav­i­ga­tion­school.co.uk and en­ter ‘trail18s’ at the check­out for your dis­count.

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