Added sites of special scientific interest (SSSI) within Trafford.

sites_of_special_scientific_interest/README.md

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+<table>
+<tr>
+	<td>Dataset name</td>
+	<td>Sites of Special Scientific Interest (SSSI) in Trafford</td>
+</tr>
+<tr>
+	<td>Dataset description</td>
+	<td>A Site of Special Scientific Interest (SSSI) is the land notified as an SSSI under the Wildlife and Countryside Act (1981), as amended. Sites notified under the 1949 Act only are not included in the Data set. SSSI are the finest sites for wildlife and natural features in England, supporting many characteristic, rare and endangered species, habitats and natural features. The data do not include "proposed" sites. Boundaries are generally mapped against Ordnance Survey MasterMap.</td>
+</tr>
+<tr>
+	<td>Source</td>
+	<td>Natural England</td>
+</tr>
+<tr>
+	<td>Publisher</td>
+	<td>Natural England</td>
+</tr>
+<tr>
+	<td>Publisher URL</td>
+	<td><a href="https://www.data.gov.uk/dataset/5b632bd7-9838-4ef2-9101-ea9384421b0d/sites-of-special-scientific-interest-england#licence-info"></a>	https://www.data.gov.uk/dataset/5b632bd7-9838-4ef2-9101-ea9384421b0d/sites-of-special-scientific-interest-england#licence-info</td>
+</tr>
+<tr>
+	<td>Geography</td>
+	<td>Local authority</td>
+</tr>
+<tr>
+	<td>Geographic coverage</td>
+	<td>Trafford</td>
+</tr>
+<tr>
+	<td>Temporal coverage</td>
+	<td>2024-07-29</td>
+</tr>
+<tr>
+	<td>Update frequency</td>
+	<td>Unknown</td>
+</tr>
+<tr>
+	<td>Licence</td>
+	<td><a href="http://www.nationalarchives.gov.uk/doc/open-government-licence/version/3/">Open Government Licence</a></td>
+</tr>
+<tr>
+	<td>Attribution</td>
+	<td>&copy; Natural England copyright. Contains Ordnance Survey data &copy; Crown copyright and database right [year].</td>
+</tr>
+<tr>
+	<td>Format</td>
+	<td>GeoJSON</td>
+</tr>
+<tr>
+	<td>Openness rating</td>
+	<td>&#9733&#9733&#9733&#9734&#9734&nbsp; Structured data in open format (e.g. CSV)</td>
+</tr>
+<tr>
+	<td>Last updated</td>
+	<td>2024-08-14</td>
+</tr>
+<tr>
+	<td>Notes</td>
+	<td></td>
+</tr>
+<tr>
+	<td>Lab visualisation</td>
+	<td>View data within the Lab's <a href="https://www.trafforddatalab.io/explore/#dataset=sssi">Explore application</a>.</td>
+</tr>
+</table>

sites_of_special_scientific_interest/pre-processing.R

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+# Sites of Special Scientific Interest (SSSI) in Trafford
+# Created 2024-08-13
+# Data updated: 2024-07-23
+# Data: https://naturalengland-defra.opendata.arcgis.com/datasets/Defra::sites-of-special-scientific-interest-england/about
+# Metadata: https://www.data.gov.uk/dataset/5b632bd7-9838-4ef2-9101-ea9384421b0d/sites-of-special-scientific-interest-england
+# Licence: Open Government Licence v3 (https://www.data.gov.uk/dataset/5b632bd7-9838-4ef2-9101-ea9384421b0d/sites-of-special-scientific-interest-england#licence-info)
+
+# NOTES:
+# These features are obtained from an ArcGIS API service, similar to that of the ONS Geography Portal.
+# The default API call returns features for the whole county, therefore it's best to use some extra parameters, such as defining a rectangle (spatial envelope) around the LA, to reduce the amount of data being returned and speed up the process.
+
+
+# Required packages ---------
+library(tidyverse) ; library(sf)
+
+# =========
+# VERY IMPORTANT NOTE REGARDING SF PACKAGE AND COORDINATE WINDING ORDER 2023-12-21:
+# The IETF standard for GeoJSON has made certain changes over the original non-IETF specification.  The changes can be viewed here: https://datatracker.ietf.org/doc/html/rfc7946#appendix-B
+# One key change is that polygon rings MUST follow the right-hand rule for orientation (counter-clockwise external rings, clockwise internal rings).
+# This change has caused issues with certain libraries which have historically used the left-hand rule, i.e. clockwise for outer rings and counter-clockwise for interior rings.
+# D3-Geo, Vega-Lite and versions of sf below 1.0.0 (default behaviour) use the GEOS library for performing flat-space calculations, known as R^2 (R-squared) which produce polygons wound to the left-hand rule.
+# The sf package from version 1.0.0 onwards now uses the S2 library by default which performs S^2 (S-squared) spherical calculations and returns polygons wound according to the right-hand rule.
+# At the time of writing, if we want our geography files to work in D3 and Vega-Lite, they must use the left-hand rule and so we need sf to use the GEOS library not S2.
+# More information regarding this can be found at: https://r-spatial.github.io/sf/articles/sf7.html#switching-between-s2-and-geos
+# =========
+sf_vers <- package_version(packageVersion('sf')) # packageVersion returns a character string, package_version converts that into numeric version numbers (major.minor.patch) e.g. 1.0.0
+
+# Only run the following if we are using sf version 1.0.0 or above
+if (sf_vers$major >= 1) {
+    useS2 <- sf_use_s2()    # store boolean to indicating if sf is currently using the s2 spherical geometry package for geographical coordinate operations
+    sf_use_s2(FALSE)        # force sf to use R^2 flat space calculations using GEOS which returns polygons with left-hand windings
+}
+
+
+# API parameters specifying the spatial rectangular area containing Trafford
+api_geommetry_envelope <- "&geometryType=esriGeometryEnvelope&geometry=%7B%22spatialReference%22%3A%7B%22latestWkid%22%3A3857%2C%22wkid%22%3A102100%7D%2C%22xmin%22%3A-278455.35481123265%2C%22ymin%22%3A7047642.057770884%2C%22xmax%22%3A-244823.0623658004%2C%22ymax%22%3A7073592.428873666%2C%22type%22%3A%22esriGeometryEnvelope%22%7D"
+
+
+# Local authority district -------------------------
+# Source: ONS Open Geography Portal
+# URL: https://geoportal.statistics.gov.uk/datasets/ons::local-authority-districts-may-2023-boundaries-uk-bgc/about
+# Licence: OGL v3.0
+# NOTE: we need the LA boundary stored as an sf object for use in st_intersection() calculations for other boundaries/features
+la <- st_read("https://services1.arcgis.com/ESMARspQHYMw9BZ9/arcgis/rest/services/Local_Authority_Districts_May_2023_UK_BGC_V2/FeatureServer/0/query?outFields=*&where=UPPER(lad23cd)%20like%20%27%25E08000009%25%27&f=geojson") %>%
+  select(area_code = LAD23CD, area_name = LAD23NM)
+
+
+# Get the SSSI information for areas within Trafford -------------------------
+df_sssi <- st_read(paste0("https://services.arcgis.com/JJzESW51TqeY9uat/arcgis/rest/services/SSSI_England/FeatureServer/0/query?outFields=*&where=1%3D1&f=geojson", api_geommetry_envelope)) %>% 
+  st_intersection(la)
+
+# Process the dataset, renaming and creating required variables
+df_sssi <- df_sssi %>%
+    rename(site_name = SSSI_NAME,
+           site_area_hectares = SSSI_AREA,
+           site_area_square_metres = Shape__Area,
+           natural_england_site_information_system_id = ENSISID,
+           british_national_grid_reference = REFERENCE) %>%
+    # Calculate and store the coordinates of each locality's centroid as a "lat" and "lon" property
+    mutate(lon = map_dbl(geometry, ~st_centroid(.x)[[1]]),
+           lat = map_dbl(geometry, ~st_centroid(.x)[[2]]),
+           site_area_hectares = as.numeric(str_trim(format(site_area_hectares, nsmall = 2))),
+           site_area_square_metres = as.numeric(str_trim(format(site_area_square_metres, nsmall = 2)))) %>%
+    select(site_name,
+           site_area_hectares,
+           site_area_square_metres,
+           natural_england_site_information_system_id,
+           british_national_grid_reference,
+           lon,
+           lat)
+
+
+# Create the SSSI file for Trafford -------------------------
+st_write(df_sssi, "trafford_sites_of_special_scientific_interest.geojson")
+
+
+# Ensure sf_use_s2() is reset to the state it was in before running the code above, i.e. whether to use the S2 library (for S^2 spherical coordinates) or GEOS (for R^2 flat space coordinates). Only if using v1 or above of the sf package
+if (sf_vers$major >= 1) sf_use_s2(useS2)