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Using Grab a Grid Reference - dual map version

The maps below provide Ordnance Survey (OS) grid references and a range of site boundaries for use with surveying and recording wildlife in the Somerset. The maps are based on the Grab a Grid Reference site by Keith Balmer at Bedfordshire Natural History Society and adapted for use in Somerset by SERC (see Acknowledgements, below).

On devices with GPS and newer browsers - e.g. smartphones - you may be able to use the device's built-in geolocation. Check out the using geolocation button below for more details. Otherwise you can proceed without using the geolocation facility.

Drag the red marker on the left-hand map to where you want a grid reference (see below for more about grid refs). The blue marker on the right-hand map tracks the red marker and cannot be dragged. It also tracks the zoom level - but note that the Google map on the left will zoom in closer than the OS maps. The grid references will appear in the grey box below and the corresponding size and colour of grid square is drawn on both maps.

Tick your choice(s) of grid reference from the grey box. Click the "About grid references" button for more information. Note that the grey box also has a full digital Easting/Northing option, plus a Lat/Long option, for checking e.g. against GPS readings.

Clicking on "Get the marker" will bring it to the centre of the map. If you pan away from the marker, click "Go to marker" to get back to it.

Additional boundary layers can be ticked on and off. These only show on the left map. Note that the more detailed layers may load slowly and take a while to appear, especially on older systems or slower internet connections.

The right-hand map shows Ordnance Survey maps of different scales according to the zoom level. This includes the nice OS Landranger maps familiar to walkers and tourists. Ordnance Survey limits the number of map tiles that may be accessed per day, so their map will stop working if this is reached.

The right-hand map copies the position of the left-hand map whenever it is zoomed, panned or the marker moves, but the right map can be can be zoomed and panned on its own. If you've found the place you wanted using the right map, you can move the left map to it using the "Match Left Map to Right Map" button. The "Get The Marker" button moves the marker to the centre of the left map, so you may want to match the maps first.

The right-hand map also has a coordinates tracker in the bottom left corner. You can use this to get a quick idea of your changing OS grid reference, by substituting the main letter prefixes for the first number of each coordinate - for example, Easting:2xxxxx,Northing:4xxxxx lies within the SC 100km square, so a reading of E:228600, N:470000 is equivalent to SC286700. Likewise NX=2-5-

The Search for: box can be used to search for locations, either by a Grid reference (e.g. SC340959), postcode (e.g. IM5 1AU), or a placename - but note that it currently goes to the first matched placename rather than a choice, so you might prefer to use postcodes where available.

As with most online maps, you will need to have Javascript enabled to get the benefit of this page. Without it the maps will be blank, the info boxes won't hide on clicking and the tools won't work. It won't normally be a problem, as most browsers have Javascript enabled by default. If not, you should be able to enable it in the Settings menu of your browser.

Grab a Grid Ref has been tested on a range of browsers and found to work on all except earlier versions of Internet Explorer (v9 and earlier). Earlier versions are functional but the site layout may be a bit sketchy-looking. Mobile browsers will work but may look a little cramped on a small screen.

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Got GPS? Want to find your current grid reference?
Double-click the button to move the map to your current GPS location:

!Check that the GPS location looks right before using the grid reference; you may want to drag the marker to a more accurate position first. For more information click the "using geolocation" button below.
 Map controls Checking tile count...

OS Grid References
The grid references below mark the position of the colour-coded grid square around the red marker on the left-hand map. Drag the marker to where you want the reference, or centre the map on the desired place and click "Get the marker".
10m square (8-figure reference)
100m square (6-figure reference)
1km square (4-figure reference)
2km square (tetrad reference)
10km square (for atlas use, not field survey)
Easting, Northing (full digital reference)
WGS84 Lat/Long (used by most GPS units)

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Using geolocation with Grab a Grid Reference

Click on the geolocate now button to centre the Google map on your current location.
If the new location (i.e. centre of the map) looks OK, click a second time to centre the marker and show the grid reference.

If you haven't done this before, a box will come up, either asking you to share your location, or asking about Google's Location Services, or similar. Only a good built-in GPS is worth using to get a grid reference. Location Services will work even on computers with no GPS, but only by locating your Internet Provider or IP address. Whilst this can be very accurate, it might just dump the marker in the next town where your IP is located! Even a good GPS can be inaccurate if the signal is weak or non-existent, so always check the marker location carefully before using an automatic geolocation to get a grid reference! You may need to drag the marker a bit to get a true position, especially where GPS signals are poor.

More information
If all you need is a mobile grid reference finder on an Android phone or tablet, we recommend using the Grid Reference - British Isles app, available from the Google Play store here. A range of mapping apps with grid references, for Apple and Android devices, may also be downloaded from Ordnance Survey directly here.

The same geolocation feature familiar to users of Google Maps on smartphones and tablets is built into Grab a Grid Ref, but will only work with the more up-to-date web browsers. Older or more "lightweight" browsers will give a message to say geolocation is not available.

On a suitable browser you will still need to have "location services" enabled under your phone or tablet settings. When you click on the geolocate now button, you will probably get a message asking if you want to enable/share your location. Tick "Yes" to proceed with geolocation. Otherwise you can just carry on without it. Bear in mind the note above about the more vague kinds of location services; it is usually best to do without if no GPS signal is available.

You don't have to use your current location if you actually want a reference for somewhere else, even if you do have geolocation enabled. Just drag the marker to wherever you want.

The marker won't automatically track your location - it needs to be independent to allow it to be dragged about. However, you can get the marker back to your current location at any time by clicking on geolocate now again to re-centre the map. Then click again (or click Get the Marker) to move the marker to your current position.

Not all mobile browsers are new, or complex, enough to read automatic geolocation. Our current recommendation would be Puffin Browser. You may need to experiment with which mobile browser gives the best performance on your phone or tablet.

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About the map layers

Tick or untick the extra map layers as required. Click on the features to get a brief name, area or description. Some features also have links to websites with more information. Note that the most recently-ticked layer is the "top" layer: if the top feature obscures the layer underneath, clicking on it will get you information for the top layer only.

See Acknowledgements and Copyright, below, for conditions of use of the various layers.

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Ordnance Survey grid references

Grab a Grid Reference maps are designed to help biological recorders get British Ordnance Survey grid references from online maps. Most online maps do not use an OS grid projection, but it is possible to get converted coordinates, accurate to within a few metres.

The Ordnance Survey website has a useful page of information and FAQs about their national grid system here.

OS grid references are entirely grid-based; thus, a reference is for a square, not a point as such. This needs to be borne in mind when looking at "point" grid references plotted on a map. The size of the square - e.g. the commonly-used 100mx100m 6-figure grid reference - relates to recording accuracy and purpose. Experienced recorders avoid artificially detailed references (e.g. 12-figure coordinates, apparently accurate to 10cm, taken from a GPS where the record itself is really for a whole field). Likewise, 2km and 10km square grid references are too vague for most local recording purposes. Such references are, however, useful for atlas distribution maps and large-scale systematic surveys.

We recommend using a 6-figure or 8-figure grid reference for local sightings wherever possible.

If you'd like more technical detail, or are curious about the difference projection types, A Guide to Coordinate Systems in Great Britain (click to download a pdf document) is quite a comprehensive guide.

For those wanting to use these maps further afield: although the OSGB National Grid covers a portion of Ireland, Irish grid references are usually given using a different system. Irish grid refs can be obtained here.