Coastal zone data
NGD data within the coastal zone
During this tutorial we will be exploring OS National Geographic Database (NGD) attributes to get insight about features within the coastal zone. This may be useful if you require an understanding what types of features lie within the coastal zone and when they last changed.
The coastal zone is made up of a variety of real world features, such as beaches (e.g. sand, shingle), vegetation (e.g. salt marsh), rivers/stream that flow into the sea, rocky outcrops etc., some of which are always wet, some that are always dry and some that are sometimes wet and sometimes dry.
So lets see how we can identify those with OS NGD data.
The following OS NGD Themes are used in this tutorial: OS NGD Land OS NGD Water
The OS NGD Land > Land feature type (fts) contains features depicting Land Cover information which can be either manmade (e.g. slipway) or natural (e.g. sand).
It looks a bit like a 'swiss cheese' or a jigsaw puzzle, but missing a few pieces as features like buildings, pavements and roads are not present, those are in OS NGD Buildings and OS NGD Transport themes instead.
Note
The base map does not fully match the tidal update to the OS NGD Land and Water themes, that's because they were on a different publication cycle during the time this tutorial was created.
By classifying on oslandcovertiera attribute, we can quickly ascertain the higher level classes of land cover in the area north of St. Andrews, e.g. made or vegetation.
Tip: For more detailed classes, such as sand or coniferous trees, use the oslandcovertierb or description attributes.
However, we may only be interested in features within the coastal zone.
This is where we utilise the 'istidal' attribute, a Boolean value which indicates whether a feature lies in the intertidal zone affected by normal tides. In other words, areas of land between Mean High Water (Springs) and Mean Low Water (Springs).
"istidal" = trueThe result only shows OS NGD Land features affected by tides.
This may be useful in calculating the extent of change between two epochs of the data to understand potential loss or gain, such as due to accretion or erosion.
Moving onto the OS NGD Water theme, we may be interested in understanding when OS tidelines were last updated.
OS NGD data gives greater insight into when a feature was initially captured, last updated along with the latest evidence date information.
Many coastlines can be quite dynamic in nature, one could say that in many areas the change is continuous as the tidal mark position is constantly shifting. Therefore it is often not practical nor possible to update the tidelines and coastal zone as frequently as they change in the real world, instead we update at periodic intervals which provide snapshots in time according to when a survey was carried out.
Sometimes the time period between the evidence date (e.g. date of survey or imagery capture) and the update date (e.g. the date the features are updated in the data) can be days or even months apart, this is very much depending on how the feature was captured in the real world and the level of processing required to add the feature into the OS NGD database.
By looking at previous versions of the tideline data, we can now start to build a picture to see how, in this example, the Eden Estuary (Fife) foreshore and sand banks have changed over time.
If you are interested in a real life use case that informs future policy decisions within the coastal zone, check out Scotland's Dynamic Coast reports and maps.
This story map has been created using the following data:
- OS NGD Land - Land Features - Land
- OS NGD Water - Water Features - Tidal Boundary
Further detail about these can be found on the OS website product pages.
The logo in the top left of this story map will take you to the main OS website homepage.
More story map examples like this once can be found in the More Than Maps site.
