spoons
Joined: 09 Jan 2007
Posts: 4991
Location: St John's Town of Dalry
|
 Posted: Mon May 12, 2014 7:49 pm Post subject: Location Data |
 |
|
If you just want the easiest way to get a 10 digit NGR then skip to the last paragraph.
National Grid Reference (NGR)
A NGR is in two parts, the first part is two character ‘grid letters’ and each pair of grid letters describes a 100km by 100km square on an Ordnance Survey map. For example NX covers most of Galloway. The second part is the ‘digits’ which can be 4, 6, 8 or 10 which give increasing levels of accuracy.
A 4 digit NGR describes a 1km by 1km square, 6 digits a 100m by 100m square, 8 digits is a 10m by 10m square and 10 digits a 1m square. The first half of the digits describes the ‘easting’ and the second part the ‘northing’ i.e. the distance to the East and North of the starting point (of the grid letter pair). A NGR must have both the letters and digits and is usually referred to as being a 6 (or 4 or 8 or 10) figure grid reference.
For example NX 619 811 describes a 100m by 100m square of St John’s Town of Dalry and finding an item on the ground within that square would depend on how obvious it was. Whereas NX 61927 81138 would define the location of the War Memorial within one metre in either direction.
NGRs can be written with or without spaces. The greatest accuracy that can be obtained by using a paper map is a six figure grid reference whereas a GPS (or smartphone app) can provide a 10 figure grid reference. Be aware however that a GPS or smartphone will only be accurate to between 6 and 10 metres depending on how many satellites can be picked up.
Latitude and longitude
Using latitude and longitude is an alternative method of pinpointing the exact location of a specific place on the earth’s surface and is commonly used by satellite positioning systems and GPS devices. Latitude specifies the north-south position of a point and longitude the east-west position.
Latitude defines the number of degrees above (plus) or below (minus) the equator. Longitude is measured in degrees East (plus) or West (minus) of the Greenwich meridian. Traditionally, degrees, minutes and seconds were used but it is now more normal to use decimal degrees.
You may come across the abbreviated version of the terms ‘lat-long’. For an example of a latitude and longitude reference ‘55.105367 -4.165778’ is the war memorial in St John’s Town of Dalry.
Conversion.
It is possible to convert directly from NGR to lat-long and vice-versa. One way of doing this is the website
http://www.nearby.org.uk/conversions.cgi
A note about Post Codes
Post codes do not define a geographical point or area but are a list of addresses to which mail can be delivered. Sometimes this can be a post box and be somewhat distant from the addressees premises. There are also instances where a new building can retain the postcode of the previous building even if it is a little way distant so any location system (e.g. car satnav) using Post Code data has built in inaccuracies. Of course, remote locations such as fields, forests and the top of hills do not have a postcode.
To find out more about location data, go to http://www.ordnancesurvey.co.uk/blog/2013/03/map-reading-skills-learn-how-to-use-grid-references/
To obtain a 10 figure Grid Ref
If you have a smartphone, the easiest way to get a 10 figure grid ref (NGR) of your current location is to use the free app ‘Grid Ref’ – just press the button and it is there on the screen. Failing that, when you are back at home, go to http://gridreferencefinder.com then right click to get the info you need.
\Paul |
|
FAQ
Search
Memberlist
Usergroups
Register
Profile
Log in to check your private messages
Log in
