# Using the NGD Features API with R

The National Geographic Database (NGD) Features API provides access to Ordnance Survey’s next generation NGD data. The NGD Features API is a premium or public sector product only. The NGD Features API allows for programmatic access to NGD data in `GeoJSON` format. For `R` developers, `osdatahub` library wraps the functionality of the NGD Features API to make it easy to get data from Ordnance Survey.

> Not using `R`? There are Python and JavaScript versions of `osdatahub`.

## 1. Getting Started

### Importing the `osdatahub` package

Once the package is installed within `R`, import the library.

    library(osdatahub)

### Importing your OS Data Hub API Key

In order to access the NGD, you must first have an OS Data Hub API key. A notebook explaining the process of registering an account and getting an API key is available to read here. When you’re choosing which APIs you want to add to your project, you must select “OS NGD API - Features” to use NGD data.

Once you have an API key, you can load your API key in by either passing it in as a string to functions in `osdatahub`, or setting it as an environment variable. While you can store your API key as a string variable in your scripts, you want to protect your API key and not share it with others.

    # Option 1.
    # Create an environment variable with your API key.
    # This function is available in the osdatahub package.
    set_os_key('YOUR API KEY HERE')

Alternatively, you can add the environment variable manually in a file called `.Renviron`, typically in your home directory.

    # Option 2.
    # Enter the following command in the R console.
    file.edit("~/.Renviron")

The file looks something like:

    VAR1 = value1
    VAR2 = value2

Add a variable named: `OS_API_KEY`. Note that `.Renviron` is processed on start-up, so restart `R` to see changes. Environment variables are available in every running R process, and can be read by any other program on your computer. More secure options see the `keyring` package.

### Import the `osdatahub` package

To access the NGD API functions from `osdatahub`, write the following:

    library(osdatahub)

## 2. Discovering Collections

The NGD contains multiple themes and collections:

- A `theme` is a family of `collections`, for example, there is a theme called ‘Buildings’.
- A `collection` is a group of features. The Buildings theme contains two collections: ‘BuildingLine’ and ‘BuildingPart’.

You can read more about the NGD Features API’s themes and collections in the Technical Specification.

To quickly retrieve a data frame of available data, you can query the API directly:

    ngd_collections <- list_ngd_collections(simple = FALSE)

This will returna a data.frame object, which we can then iterate through to return metadata about each collection.

    for(i in 1:nrow(ngd_collections)){
      collection <- ngd_collections[i, ]

      print(paste0(collection$title, '(', collection$id, ')'))
    }
    #> [1] "Building v1(bld-fts-building-1)"
    #> [1] "Building Line v1(bld-fts-buildingline-1)"
    #> [1] "Building Part v1(bld-fts-buildingpart-1)"
    #> [1] "Named Area v1(gnm-fts-namedarea-1)"
    #> [1] "Named Point v1(gnm-fts-namedpoint-1)"
    #> [1] "Land v1(lnd-fts-land-1)"
    #> [1] "Landform v1(lnd-fts-landform-1)"
    #> [1] "Landform Line v1(lnd-fts-landformline-1)"
    #> [1] "Landform Point v1(lnd-fts-landformpoint-1)"
    #> [1] "Land Point v1(lnd-fts-landpoint-1)"
    #> [1] "Site v1(lus-fts-site-1)"
    #> [1] "Site Access Location v1(lus-fts-siteaccesslocation-1)"
    #> [1] "Site Routing Point v1(lus-fts-siteroutingpoint-1)"
    #> [1] "Compound Structure v1(str-fts-compoundstructure-1)"
    #> [1] "Structure v1(str-fts-structure-1)"
    #> [1] "Structure Line v1(str-fts-structureline-1)"
    #> [1] "Structure Point v1(str-fts-structurepoint-1)"
    #> [1] "Cartographic Rail Detail v1(trn-fts-cartographicraildetail-1)"
    #> [1] "Rail v1(trn-fts-rail-1)"
    #> [1] "Road Line v1(trn-fts-roadline-1)"
    #> [1] "Road Track Or Path v1(trn-fts-roadtrackorpath-1)"
    #> [1] "Connecting Link v1(trn-ntwk-connectinglink-1)"
    #> [1] "Connecting Node v1(trn-ntwk-connectingnode-1)"
    #> [1] "Ferry Link v1(trn-ntwk-ferrylink-1)"
    #> [1] "Ferry Node v1(trn-ntwk-ferrynode-1)"
    #> [1] "Ferry Terminal v1(trn-ntwk-ferryterminal-1)"
    #> [1] "Path v1(trn-ntwk-path-1)"
    #> [1] "Path Link v1(trn-ntwk-pathlink-1)"
    #> [1] "Path Node v1(trn-ntwk-pathnode-1)"
    #> [1] "Pavement Link v1(trn-ntwk-pavementlink-1)"
    #> [1] "Railway Link v1(trn-ntwk-railwaylink-1)"
    #> [1] "Railway Link Set v1(trn-ntwk-railwaylinkset-1)"
    #> [1] "Railway Node v1(trn-ntwk-railwaynode-1)"
    #> [1] "Road v1(trn-ntwk-road-1)"
    #> [1] "Road Junction v1(trn-ntwk-roadjunction-1)"
    #> [1] "Road Link v1(trn-ntwk-roadlink-1)"
    #> [1] "Road Link v2(trn-ntwk-roadlink-2)"
    #> [1] "Road Node v1(trn-ntwk-roadnode-1)"
    #> [1] "Street v1(trn-ntwk-street-1)"
    #> [1] "Average And Indicative Speed v1(trn-rami-averageandindicativespeed-1)"
    #> [1] "Highway Dedication v1(trn-rami-highwaydedication-1)"
    #> [1] "Maintenance Area v1(trn-rami-maintenancearea-1)"
    #> [1] "Maintenance Line v1(trn-rami-maintenanceline-1)"
    #> [1] "Maintenance Point v1(trn-rami-maintenancepoint-1)"
    #> [1] "Reinstatement Area v1(trn-rami-reinstatementarea-1)"
    #> [1] "Reinstatement Line v1(trn-rami-reinstatementline-1)"
    #> [1] "Reinstatement Point v1(trn-rami-reinstatementpoint-1)"
    #> [1] "Restriction v1(trn-rami-restriction-1)"
    #> [1] "Routing Hazard v1(trn-rami-routinghazard-1)"
    #> [1] "RoutingStructure v1(trn-rami-routingstructure-1)"
    #> [1] "Special Designation Area v1(trn-rami-specialdesignationarea-1)"
    #> [1] "Special Designation Line v1(trn-rami-specialdesignationline-1)"
    #> [1] "Special Designation Point v1(trn-rami-specialdesignationpoint-1)"
    #> [1] "Inter Tidal Line v1(wtr-fts-intertidalline-1)"
    #> [1] "Tidal Boundary v1(wtr-fts-tidalboundary-1)"
    #> [1] "Water v1(wtr-fts-water-1)"
    #> [1] "Water Point v1(wtr-fts-waterpoint-1)"
    #> [1] "Water Link v1(wtr-ntwk-waterlink-1)"
    #> [1] "Water Link Set v1(wtr-ntwk-waterlinkset-1)"
    #> [1] "Water Node v1(wtr-ntwk-waternode-1)"

## 3. Loading NGD Data into a Spatial Data Frame

We’ll now walk through the process of acquiring data from the NGD Building Part collection (`bld-fts-buildingpart-1`) and importing this data into a an object of type `sf`.

### Requesting NGD Data

To get the first 100 features in the collection, you simply need to query use the NGD query function:

    collection <- 'bld-fts-buildingpart-1'

    # make the query and contact the API
    # reduce the number of features returned for the example
    features <- query_ngd(collection = collection, max_results = 4)

The API returns an OGC-compliant GeoJSON, which is easy to import into other libraries for analysis.

### Importing into a spatial data frame

If you haven’t already, install and import the `sf` library:

    library(sf)
    #> Linking to GEOS 3.9.1, GDAL 3.3.2, PROJ 7.2.1; sf_use_s2() is TRUE

And now, import the NGD data.

    gdf = st_read(features, quiet = TRUE)

Let’s take a look at a preview of the data using `head()`. As you’ll see, NGD data is rich in attribution:

    head(gdf)
    #> Simple feature collection with 4 features and 39 fields
    #> Geometry type: POLYGON
    #> Dimension:     XY
    #> Bounding box:  xmin: -3.97032 ymin: 51.59236 xmax: 1.727559 ymax: 55.7426
    #> Geodetic CRS:  WGS 84
    #>                                   osid                 toid     theme          changetype isobscured description versiondate geometry_area   height_source
    #> 1 000000b1-0556-4231-a52a-9b5b8b82dfbf    osgb1000041024621 Buildings Modified Attributes      FALSE    Building  2022-09-18     59.200650 Ordnance Survey
    #> 2 00000183-3ae0-4f05-adb8-a5792d09f55f osgb5000005167584940 Buildings                 New      FALSE    Building  2022-08-26      9.499142 Ordnance Survey
    #> 3 000001d6-8217-4f7a-a70e-3757eb76c9e4    osgb1000000360448 Buildings                 New      FALSE    Building  2022-08-26     15.258750 Ordnance Survey
    #> 4 00000208-a659-49f9-a587-ab26cb2b2248    osgb1000017249389 Buildings                 New      FALSE    Building  2022-08-26     12.806250 Ordnance Survey
    #>   physicallevel               oslandusetiera        oslandusetierb geometry_source oslandcovertiera oslandcovertierb oslanduse_source height_updatedate
    #> 1 Surface Level    Residential Accommodation ["Private Residence"] Ordnance Survey      Constructed     ["Building"]  Ordnance Survey        2022-08-24
    #> 2 Surface Level    Residential Accommodation ["Private Residence"] Ordnance Survey      Constructed     ["Building"]  Ordnance Survey        2022-08-24
    #> 3 Surface Level    Residential Accommodation ["Private Residence"] Ordnance Survey      Constructed     ["Building"]  Ordnance Survey        2022-08-24
    #> 4 Surface Level Unknown Or Unused Artificial                    [] Ordnance Survey      Constructed     ["Building"]  Ordnance Survey        2022-08-24
    #>   description_source oslandcover_source associatedstructure geometry_updatedate height_evidencedate capturespecification oslanduse_updatedate
    #> 1    Ordnance Survey    Ordnance Survey                <NA>          2006-08-30          2022-06-20                Urban           2006-08-30
    #> 2    Ordnance Survey    Ordnance Survey                <NA>          2015-10-29          2022-04-16                Rural           2015-10-29
    #> 3    Ordnance Survey    Ordnance Survey                <NA>          1993-04-01          2022-07-10                Urban           1993-04-01
    #> 4    Ordnance Survey    Ordnance Survey                <NA>          1993-05-01          2022-02-27                Urban           1993-05-01
    #>   absoluteheightmaximum absoluteheightminimum geometry_evidencedate heightconfidencelevel relativeheightmaximum absoluteheightroofbase description_updatedate
    #> 1                115.16                105.00            2006-08-30          Not Assessed                 10.16                 110.85             2006-08-30
    #> 2                  7.29                  5.39            2015-03-11          Not Assessed                  1.90                   6.21             2015-10-29
    #> 3                 38.63                 34.70            1993-04-01          Not Assessed                  3.93                  37.13             1993-04-01
    #> 4                 72.80                 69.99            1993-05-01          Not Assessed                  2.81                  71.95             1993-05-01
    #>   oslandcover_updatedate oslanduse_evidencedate relativeheightroofbase versionavailabletodate firstdigitalcapturedate description_evidencedate
    #> 1             2006-08-30             2006-08-30                   5.85                   <NA>              1991-09-18               2006-08-30
    #> 2             2015-10-29             2015-03-11                   0.82                   <NA>              2015-11-12               2015-03-11
    #> 3             1993-04-01             1993-04-01                   2.43                   <NA>              1993-04-01               1993-04-01
    #> 4             1993-05-01             1993-05-01                   1.96                   <NA>              1993-05-01               1993-05-01
    #>   oslandcover_evidencedate versionavailablefromdate                       geometry
    #> 1               2006-08-30      2022-09-19 01:00:00 POLYGON ((-3.970308 55.7425...
    #> 2               2015-03-11      2022-08-27 01:00:00 POLYGON ((1.727559 52.66142...
    #> 3               1993-04-01      2022-08-27 01:00:00 POLYGON ((0.1941514 51.5924...
    #> 4               1993-05-01      2022-08-27 01:00:00 POLYGON ((-1.454721 52.3961...

Alternatively, it’s possible to return an `sf` object directly from the NGD query function:

    # retrieve features and automatically convert to spatial data frame
    features <- query_ngd(collection = collection,
                          max_results = 4,
                          returnType = 'sf')

    head(features)
    #> Simple feature collection with 4 features and 39 fields
    #> Geometry type: POLYGON
    #> Dimension:     XY
    #> Bounding box:  xmin: -3.97032 ymin: 51.59236 xmax: 1.727559 ymax: 55.7426
    #> Geodetic CRS:  WGS 84
    #>                                   osid                 toid     theme          changetype isobscured description versiondate geometry_area   height_source
    #> 1 000000b1-0556-4231-a52a-9b5b8b82dfbf    osgb1000041024621 Buildings Modified Attributes      FALSE    Building  2022-09-18     59.200650 Ordnance Survey
    #> 2 00000183-3ae0-4f05-adb8-a5792d09f55f osgb5000005167584940 Buildings                 New      FALSE    Building  2022-08-26      9.499142 Ordnance Survey
    #> 3 000001d6-8217-4f7a-a70e-3757eb76c9e4    osgb1000000360448 Buildings                 New      FALSE    Building  2022-08-26     15.258750 Ordnance Survey
    #> 4 00000208-a659-49f9-a587-ab26cb2b2248    osgb1000017249389 Buildings                 New      FALSE    Building  2022-08-26     12.806250 Ordnance Survey
    #>   physicallevel               oslandusetiera        oslandusetierb geometry_source oslandcovertiera oslandcovertierb oslanduse_source height_updatedate
    #> 1 Surface Level    Residential Accommodation ["Private Residence"] Ordnance Survey      Constructed     ["Building"]  Ordnance Survey        2022-08-24
    #> 2 Surface Level    Residential Accommodation ["Private Residence"] Ordnance Survey      Constructed     ["Building"]  Ordnance Survey        2022-08-24
    #> 3 Surface Level    Residential Accommodation ["Private Residence"] Ordnance Survey      Constructed     ["Building"]  Ordnance Survey        2022-08-24
    #> 4 Surface Level Unknown Or Unused Artificial                    [] Ordnance Survey      Constructed     ["Building"]  Ordnance Survey        2022-08-24
    #>   description_source oslandcover_source associatedstructure geometry_updatedate height_evidencedate capturespecification oslanduse_updatedate
    #> 1    Ordnance Survey    Ordnance Survey                <NA>          2006-08-30          2022-06-20                Urban           2006-08-30
    #> 2    Ordnance Survey    Ordnance Survey                <NA>          2015-10-29          2022-04-16                Rural           2015-10-29
    #> 3    Ordnance Survey    Ordnance Survey                <NA>          1993-04-01          2022-07-10                Urban           1993-04-01
    #> 4    Ordnance Survey    Ordnance Survey                <NA>          1993-05-01          2022-02-27                Urban           1993-05-01
    #>   absoluteheightmaximum absoluteheightminimum geometry_evidencedate heightconfidencelevel relativeheightmaximum absoluteheightroofbase description_updatedate
    #> 1                115.16                105.00            2006-08-30          Not Assessed                 10.16                 110.85             2006-08-30
    #> 2                  7.29                  5.39            2015-03-11          Not Assessed                  1.90                   6.21             2015-10-29
    #> 3                 38.63                 34.70            1993-04-01          Not Assessed                  3.93                  37.13             1993-04-01
    #> 4                 72.80                 69.99            1993-05-01          Not Assessed                  2.81                  71.95             1993-05-01
    #>   oslandcover_updatedate oslanduse_evidencedate relativeheightroofbase versionavailabletodate firstdigitalcapturedate description_evidencedate
    #> 1             2006-08-30             2006-08-30                   5.85                   <NA>              1991-09-18               2006-08-30
    #> 2             2015-10-29             2015-03-11                   0.82                   <NA>              2015-11-12               2015-03-11
    #> 3             1993-04-01             1993-04-01                   2.43                   <NA>              1993-04-01               1993-04-01
    #> 4             1993-05-01             1993-05-01                   1.96                   <NA>              1993-05-01               1993-05-01
    #>   oslandcover_evidencedate versionavailablefromdate                       geometry
    #> 1               2006-08-30     2022-09-19T00:00:00Z POLYGON ((-3.970308 55.7425...
    #> 2               2015-03-11     2022-08-27T00:00:00Z POLYGON ((1.727559 52.66142...
    #> 3               1993-04-01     2022-08-27T00:00:00Z POLYGON ((0.1941514 51.5924...
    #> 4               1993-05-01     2022-08-27T00:00:00Z POLYGON ((-1.454721 52.3961...

## 4. Adding Filters

Filters can help you limit the scope of your query using spatial, temporal and contextual parameters. The NGD Features API uses Common Query Language (CQL) to allow you to filter data using the attribution set of each collection.

- Spatial: `extent`

You can specify any polygon to query by using the functions in `osdatahub` to create extents. You can learn more about using extents here.

- Temporal: `state_datetime` and `end_datetime`

If you want to only get features that have a temporal property, you can specify date ranges to query within. If youw ant to get features for a single time, simply provide the same argument for both parameters.

- Contextual: `cql_filter`

The NGD API supports a generic filter grammar called the Common Query Language (CQL) to further filter your query using human readable commands. You can find out more about the operations that the API supports in the Queryables section of the Technical Specification. The CQL filter allows you to specify specific properties for features as well as spatial filters.

In addition, the `osdatahub` package permits you to specify the maximum number of features to return (by default, 100 features):

- `max_results`

Allows you to specify the maximum number of features you’d like to receive. Default is 100.

- `offset`

Skips past the specified number of features in the collection. Default is 0.

### Specifying an Extent (Bounding Box)

In our case, we want to get features that are only within a certain bounding box in Manchester. We can specify an extent based on the geometry, and then pass this into the query:

    extent = extent_from_bbox(c(-2.244973, 53.476620, -2.237799, 53.480525),
                              crs = 'CRS84')

    # Specify the 'extent' as the first parameter to define the type of query.
    features = query_ngd(x = extent,
                         collection = collection,
                         max_results = 4,
                         returnType = 'sf')

    # run this cell to see the contents of 'features'
    features
    #> Simple feature collection with 4 features and 39 fields
    #> Geometry type: POLYGON
    #> Dimension:     XY
    #> Bounding box:  xmin: -2.241707 ymin: 53.47689 xmax: -2.23773 ymax: 53.48008
    #> Geodetic CRS:  WGS 84
    #>                                   osid                 toid     theme          changetype isobscured description versiondate geometry_area   height_source
    #> 1 02837688-4553-4d32-87aa-10733dad9274    osgb1000024157902 Buildings                 New      FALSE    Building  2022-08-26      21.57975 Ordnance Survey
    #> 2 02c6f2c7-0e25-4224-b4a7-c62c7d476e48    osgb1000024157913 Buildings Modified Attributes      FALSE    Building  2023-06-03     441.13125 Ordnance Survey
    #> 3 0364fa8b-024a-4078-ae13-4a3e21c5e744    osgb1000024155721 Buildings                 New      FALSE    Building  2022-08-26     173.96250 Ordnance Survey
    #> 4 04b6b1d7-2a73-4173-b953-20c3ef2e6ce7 osgb5000005290155401 Buildings Modified Attributes      FALSE    Building  2022-09-26      45.44059            <NA>
    #>   physicallevel               oslandusetiera        oslandusetierb geometry_source oslandcovertiera oslandcovertierb oslanduse_source height_updatedate
    #> 1 Surface Level Unknown Or Unused Artificial                    [] Ordnance Survey      Constructed     ["Building"]  Ordnance Survey        2022-08-24
    #> 2 Surface Level  Commercial Activity: Retail                    [] Ordnance Survey      Constructed     ["Building"]  Ordnance Survey        2022-08-24
    #> 3 Surface Level Unknown Or Unused Artificial                    [] Ordnance Survey      Constructed     ["Building"]  Ordnance Survey        2022-08-24
    #> 4 Surface Level    Residential Accommodation ["Private Residence"] Ordnance Survey      Constructed     ["Building"]  Ordnance Survey              <NA>
    #>   description_source oslandcover_source associatedstructure geometry_updatedate height_evidencedate capturespecification oslanduse_updatedate
    #> 1    Ordnance Survey    Ordnance Survey                <NA>          2016-10-26          2021-04-19                Urban           1993-05-01
    #> 2    Ordnance Survey    Ordnance Survey                <NA>          2010-04-13          2021-04-19                Urban           2010-04-13
    #> 3    Ordnance Survey    Ordnance Survey                <NA>          1993-05-01          2021-04-19                Urban           1993-05-01
    #> 4    Ordnance Survey    Ordnance Survey                <NA>          2021-11-30                <NA>                Urban           2021-11-30
    #>   absoluteheightmaximum absoluteheightminimum geometry_evidencedate heightconfidencelevel relativeheightmaximum absoluteheightroofbase description_updatedate
    #> 1                 68.98                 43.34            2016-10-04          Not Assessed                 25.64                  66.54             1993-05-01
    #> 2                 67.69                 44.22            2010-04-13          Not Assessed                 23.47                  60.87             2010-04-13
    #> 3                 57.17                 42.16            1993-05-01          Not Assessed                 15.01                  52.83             1993-05-01
    #> 4                    NA                    NA            2021-11-30                  <NA>                    NA                     NA             2021-11-30
    #>   oslandcover_updatedate oslanduse_evidencedate relativeheightroofbase versionavailabletodate firstdigitalcapturedate description_evidencedate
    #> 1             1993-05-01             1993-05-01                  23.20                   <NA>              1993-05-01               1993-05-01
    #> 2             2010-04-13             2010-04-13                  16.65                   <NA>              1993-05-01               2010-04-13
    #> 3             1993-05-01             1993-05-01                  10.67                   <NA>              1993-05-01               1993-05-01
    #> 4             2021-11-30             2021-11-30                     NA                   <NA>              2021-11-30               2021-11-30
    #>   oslandcover_evidencedate versionavailablefromdate                       geometry
    #> 1               1993-05-01     2022-08-27T00:00:00Z POLYGON ((-2.240982 53.4790...
    #> 2               2010-04-13     2023-06-04T00:00:00Z POLYGON ((-2.241351 53.4798...
    #> 3               1993-05-01     2022-08-27T00:00:00Z POLYGON ((-2.240074 53.4781...
    #> 4               2021-11-30     2022-09-27T00:00:00Z POLYGON ((-2.23773 53.47692...

### Custom Paging Parameters

By default, `osdatahub` will return a maximum 100 features to a query - starting at zero. This behaviour can be altered by specifying `max_results` and `offset` parameters. We’ll be building on the previous example, specifying the same extent as before…

    # returns a maximum of 4 results (features 1 to 4)
    features = query_ngd(extent,
                         collection = collection,
                         max_results = 4)

    # returns a maximum of 4 results (features 101 to 104)
    features = query_ngd(extent,
                         collection = collection,
                         offset = 100,
                         max_results = 4,
                         returnType = 'sf')

    # run this cell to see the contents of 'features'
    features
    #> Simple feature collection with 4 features and 39 fields
    #> Geometry type: POLYGON
    #> Dimension:     XY
    #> Bounding box:  xmin: -2.2437 ymin: 53.47765 xmax: -2.238997 ymax: 53.47982
    #> Geodetic CRS:  WGS 84
    #>                                   osid                 toid     theme changetype isobscured description versiondate geometry_area   height_source physicallevel
    #> 1 4e1a5c52-aa3f-4c99-a216-f3ad0b5aff83    osgb1000024155766 Buildings        New      FALSE    Building  2022-08-26      64.48625 Ordnance Survey Surface Level
    #> 2 50b0ab14-2a1a-41ae-8425-6ddafbddb575    osgb1000024155767 Buildings        New      FALSE    Building  2022-08-26     457.61400 Ordnance Survey Surface Level
    #> 3 52335576-4e7b-47f8-ab79-a644172032f0    osgb1000024155700 Buildings        New      FALSE    Building  2022-08-26     166.62625 Ordnance Survey Surface Level
    #> 4 537d6ba9-5902-4e6b-b193-ad604a1570b9 osgb1000002517038005 Buildings        New      FALSE    Building  2022-08-26    1018.93900 Ordnance Survey Surface Level
    #>                 oslandusetiera oslandusetierb geometry_source oslandcovertiera oslandcovertierb oslanduse_source height_updatedate description_source
    #> 1  Commercial Activity: Retail             [] Ordnance Survey      Constructed     ["Building"]  Ordnance Survey        2022-08-24    Ordnance Survey
    #> 2  Commercial Activity: Retail             [] Ordnance Survey      Constructed     ["Building"]  Ordnance Survey        2022-08-24    Ordnance Survey
    #> 3 Unknown Or Unused Artificial             [] Ordnance Survey      Constructed     ["Building"]  Ordnance Survey        2022-08-24    Ordnance Survey
    #> 4 Unknown Or Unused Artificial             [] Ordnance Survey      Constructed     ["Building"]  Ordnance Survey        2022-08-24    Ordnance Survey
    #>   oslandcover_source associatedstructure geometry_updatedate height_evidencedate capturespecification oslanduse_updatedate absoluteheightmaximum
    #> 1    Ordnance Survey                <NA>          1993-05-01          2021-04-19                Urban           1993-05-01                 63.80
    #> 2    Ordnance Survey                <NA>          2002-10-08          2021-04-19                Urban           2002-10-08                 69.45
    #> 3    Ordnance Survey                <NA>          2010-04-28          2021-04-19                Urban           2010-04-28                 63.78
    #> 4    Ordnance Survey                <NA>          2007-03-22          2021-04-19                Urban           2007-03-22                 70.57
    #>   absoluteheightminimum geometry_evidencedate heightconfidencelevel relativeheightmaximum absoluteheightroofbase description_updatedate oslandcover_updatedate
    #> 1                 41.84            1993-05-01          Not Assessed                 21.96                  62.62             1993-05-01             1993-05-01
    #> 2                 41.20            2002-10-08          Not Assessed                 28.25                  61.31             2002-10-08             2002-10-08
    #> 3                 42.59            2010-04-28          Not Assessed                 21.19                  61.16             2010-04-28             2010-04-28
    #> 4                 41.34            2007-03-22          Not Assessed                 29.23                  59.01             2007-03-22             2007-03-22
    #>   oslanduse_evidencedate relativeheightroofbase versionavailabletodate firstdigitalcapturedate description_evidencedate oslandcover_evidencedate
    #> 1             1993-05-01                  20.78                   <NA>              1993-05-01               1993-05-01               1993-05-01
    #> 2             2002-10-08                  20.11                   <NA>              1993-05-01               2002-10-08               2002-10-08
    #> 3             2010-04-28                  18.57                   <NA>              1993-05-01               2010-04-28               2010-04-28
    #> 4             2007-03-22                  17.67                   <NA>              2007-03-22               2007-03-22               2007-03-22
    #>   versionavailablefromdate                       geometry
    #> 1     2022-08-27T00:00:00Z POLYGON ((-2.241327 53.4780...
    #> 2     2022-08-27T00:00:00Z POLYGON ((-2.24123 53.47778...
    #> 3     2022-08-27T00:00:00Z POLYGON ((-2.238997 53.4783...
    #> 4     2022-08-27T00:00:00Z POLYGON ((-2.243258 53.4794...

### Applying CQL Filters

Common Query Language (CQL) filters are a handy way in which you can tailor the results of your query to match specific needs. More information on CQL filters can be found here. We can pass a filter in the API using the `filter` parameter.

    # Building off the same extent covering Manchester, filtering by buildings
    # larger than or equal to 20m^2 and with a maximum height greater than 60m.

    # At the time of writing, this returns 7 features (buildings)

    features = query_ngd(extent,
                         collection = collection,
                         cql_filter='geometry_area>=200 AND relativeheightmaximum>60',
                         returnType = 'sf')

    # run this cell to see the contents of 'features'
    features
    #> Simple feature collection with 7 features and 39 fields
    #> Geometry type: POLYGON
    #> Dimension:     XY
    #> Bounding box:  xmin: -2.243508 ymin: 53.47677 xmax: -2.237916 ymax: 53.48044
    #> Geodetic CRS:  WGS 84
    #>                                   osid                 toid     theme          changetype isobscured description versiondate geometry_area   height_source
    #> 1 40fa2462-4c01-48d4-bcf1-5179efb56027 osgb5000005134737612 Buildings                 New      FALSE    Building  2022-08-26     2122.6936 Ordnance Survey
    #> 2 41ab80d3-28ca-460f-9afe-04671aa2807a osgb1000002517080496 Buildings                 New      FALSE    Building  2022-08-26      687.8187 Ordnance Survey
    #> 3 8a98fdc7-bc44-4ac0-8c20-aac5c7ddcf30 osgb1000002517080494 Buildings                 New      FALSE    Building  2022-08-26      206.9899 Ordnance Survey
    #> 4 8ce5ac53-d4ee-492d-9b6d-56b069252cbe    osgb1000024155687 Buildings Modified Attributes      FALSE    Building  2023-06-22      748.7997 Ordnance Survey
    #> 5 a1007205-9f06-4a36-bcba-45de245d9faf osgb5000005134737702 Buildings                 New      FALSE    Building  2022-08-26      380.3845 Ordnance Survey
    #> 6 af43ce9a-18d2-47d2-9744-fdc89f7c241c osgb5000005267089134 Buildings                 New      FALSE    Building  2022-08-26     1590.4881 Ordnance Survey
    #> 7 cfe4934e-8360-40bb-81eb-5f49d240c2b8 osgb5000005275364197 Buildings Modified Attributes      FALSE    Building  2023-06-22     1143.7811 Ordnance Survey
    #>   physicallevel                                   oslandusetiera oslandusetierb geometry_source oslandcovertiera oslandcovertierb oslanduse_source
    #> 1 Surface Level Commercial Activity: Industrial Or Manufacturing             [] Ordnance Survey      Constructed     ["Building"]  Ordnance Survey
    #> 2 Surface Level                     Unknown Or Unused Artificial             [] Ordnance Survey      Constructed     ["Building"]  Ordnance Survey
    #> 3 Surface Level                     Unknown Or Unused Artificial             [] Ordnance Survey      Constructed     ["Building"]  Ordnance Survey
    #> 4 Surface Level                              Government Services             [] Ordnance Survey      Constructed     ["Building"]  Ordnance Survey
    #> 5 Surface Level                     Unknown Or Unused Artificial             [] Ordnance Survey      Constructed     ["Building"]  Ordnance Survey
    #> 6 Surface Level Commercial Activity: Industrial Or Manufacturing             [] Ordnance Survey      Constructed     ["Building"]  Ordnance Survey
    #> 7 Surface Level               Temporary Or Holiday Accommodation             [] Ordnance Survey      Constructed     ["Building"]  Ordnance Survey
    #>   height_updatedate description_source oslandcover_source associatedstructure geometry_updatedate height_evidencedate capturespecification oslanduse_updatedate
    #> 1        2022-08-24    Ordnance Survey    Ordnance Survey                <NA>          2017-09-26          2021-04-19                Urban           2014-09-26
    #> 2        2022-08-24    Ordnance Survey    Ordnance Survey                <NA>          2009-06-25          2021-04-19                Urban           2009-06-25
    #> 3        2022-08-24    Ordnance Survey    Ordnance Survey                <NA>          2009-06-25          2021-04-19                Urban           2009-06-25
    #> 4        2022-08-24    Ordnance Survey    Ordnance Survey                <NA>          2014-11-19          2021-04-19                Urban           2010-03-18
    #> 5        2022-08-24    Ordnance Survey    Ordnance Survey                <NA>          2014-10-13          2021-04-19                Urban           2014-10-13
    #> 6        2022-08-24    Ordnance Survey    Ordnance Survey                <NA>          2020-07-16          2021-04-19                Urban           2020-07-16
    #> 7        2022-08-24    Ordnance Survey    Ordnance Survey                <NA>          2021-01-13          2021-04-19                Urban           2021-01-13
    #>   absoluteheightmaximum absoluteheightminimum geometry_evidencedate heightconfidencelevel relativeheightmaximum absoluteheightroofbase description_updatedate
    #> 1                102.52                 38.65            2017-09-26          Not Assessed                 63.87                  94.76             2014-09-26
    #> 2                105.48                 43.20            2009-06-25          Not Assessed                 62.28                 100.70             2009-06-25
    #> 3                104.38                 43.17            2009-06-25          Not Assessed                 61.21                  88.38             2009-06-25
    #> 4                116.73                 43.13            2013-11-04          Not Assessed                 73.60                 109.57             2010-03-18
    #> 5                 99.96                 39.25            2014-10-13          Not Assessed                 60.71                  94.68             2014-10-13
    #> 6                102.53                 38.69            2020-07-16          Not Assessed                 63.84                  95.19             2020-07-16
    #> 7                112.00                 40.06            2021-01-13          Not Assessed                 71.94                 107.00             2021-01-13
    #>   oslandcover_updatedate oslanduse_evidencedate relativeheightroofbase versionavailabletodate firstdigitalcapturedate description_evidencedate
    #> 1             2014-09-26             2013-11-04                  56.11                   <NA>              2014-10-21               2013-11-04
    #> 2             2009-06-25             2009-06-25                  57.50                   <NA>              2009-06-25               2009-06-25
    #> 3             2009-06-25             2009-06-25                  45.21                   <NA>              2009-06-25               2009-06-25
    #> 4             2010-03-18             2010-03-18                  66.44                   <NA>              1993-05-01               2010-03-18
    #> 5             2014-10-13             2014-10-13                  55.43                   <NA>              2014-10-21               2014-10-13
    #> 6             2020-07-16             2020-07-16                  56.50                   <NA>              2020-07-16               2020-07-16
    #> 7             2021-01-13             2021-01-13                  66.94                   <NA>              2021-01-13               2021-01-13
    #>   oslandcover_evidencedate versionavailablefromdate                       geometry
    #> 1               2013-11-04     2022-08-27T00:00:00Z POLYGON ((-2.242897 53.4772...
    #> 2               2009-06-25     2022-08-27T00:00:00Z POLYGON ((-2.242983 53.4804...
    #> 3               2009-06-25     2022-08-27T00:00:00Z POLYGON ((-2.242827 53.4801...
    #> 4               2010-03-18     2023-06-23T00:00:00Z POLYGON ((-2.238278 53.4780...
    #> 5               2014-10-13     2022-08-27T00:00:00Z POLYGON ((-2.242894 53.4777...
    #> 6               2020-07-16     2022-08-27T00:00:00Z POLYGON ((-2.2422 53.47719,...
    #> 7               2021-01-13     2023-06-23T00:00:00Z POLYGON ((-2.241926 53.4779...

## 5. Conclusion

We hope this short introduction to the `osdatahub` package’s new NGD capabilities has been useful! You can find further resources to assist you on your OS API development journal at: https://github.com/OrdnanceSurvey/os-api-resources