Select an area from the top part of the panel. Note that selecting both a National Park and an AONB will result in no returns. Be careful selecting more than one of the top four options as you may restrict your results. Only English National Parks and AONBs are identified in the database.
Then select a trig point type, or leave blank for all trig points, similarly for trig point condition.
Above Ground filters all trig points you're likely to have to dig for (such as Berntsens and Buried Blocks). Select [Yes] to avoid packing a spade.
Visitable filters trig points that are classed as 'Destroyed', 'Possibly Missing' or 'Inaccessible' for whatever reason. Select [Yes] to avoid pointless searches.
The final selection will define your sort condition, sort order and the maximum number of results returned. Be careful using [All] in Max Results, it could produce a very big list!
All data is provided "as-is" with no accuracy guaranteed.
Not all trig points extracted from the OS database have height data associated with them. Some have 0m height information. What height data there is, is mainly provided for Triangulation Pillars.
Not all trig points are associated with an OS Landranger map sheet; for example “TP0338 – Revelstoke” is to be found in the TPUK database but is not in the full list of trig points downloaded as part of the Landranger sheets exercise (it should be on Sheet 201). However, it can be found in the OS database if searched by FB Number (S3393).
Height data for trig points in this database is typically only accurate to 10m, this is due to the way the data has been collated and extracted, not in any way due to the accuracy of the OS, which is of course is generally faultless.
Around 5% of Triangulation Pillars have no Landranger map number associated with them. This could be because they are in Ireland or because the pillars are destroyed or even because they are non-typical OS pillars, such as those associated with the Great Glen project.
Allocating countries to trig points is done by a combination of OS National Grid prefix letters (NH, HU, etc) and the Landranger sheet number and as such is not especially accurate where the borders of Scotland and Wales meet those of England. Where a Landranger sheet is available, this more granular data is used to determine the country, however even some Landranger sheets are shared between two countries. In this case a Wales-England or Scotland-England value is entered. In the event of no Landranger sheet number for a trig point, the two digit OSNG prefix is used, which is even less accurate than the Landranger sheet. A similar nomenclature is used here.
The sorting of trig points by hill classification is riddled with inaccuracies. In most cases matching the grid reference of a hill top and the grid reference of a trig point to find a match is impossible at even 100m accuracy (6 digit grid reference). As such I have made a match at the square level (4 digit grid reference), such that if a square contains a trig point and a Marilyn (for example) then the database reflects that as a Marilyn with a trig point, even though the trig point could be on a nearby hill. This method also leads to duplication; so a grid reference with two classified tops (not unusual, especially in particularly hilly areas) will show a trig point on both tops. Time and my data manipulation ability (or lack of it) has led to this compromise approach.