Methodology:

Coastline:

The starting point for this data was version 7.8 of the Antarctic Digital Database coastline (doi.org/10.5285/98d7c98c-b223-4774-b20e-886630632b12). Using ArcGIS Pro version 3.3.0, the data was clipped to this area of interest and every section of line was checked against current satellite imagery, and updated where necessary. The grounding line has undergone a major revision, with the majority of new data being incorporated from Wallis et al, 2024, https://doi.org/10.5194/tc-18-4723-2024 . There ar 5 fields in the attribute table of the final dataset:

* 'surface' - detailing whether the line is 'ice coastline', 'rock coastline', 'ice shelf and front' or 'grounding line'

* 'revdate' - revision date

* 'source' - the source of each section of line, mostly consisting of satellite name and ID

* 'sourcedate' - the date of the source, mostly in YYYY-MM-DD format apart from 2 sources where a year is only available

* 'lineage' - a brief description of how each section of line was created

The coordinate reference system of the data is WGS84 Antarctic Polar Stereographic, EPSG 3031.

Contours:

Using ArcGIS Pro version 3.3.0, contours were extracted from two different Digital Elevation Models and then merged together into 1 file. The majority of contours were created from REMA v2 (Howat, Ian, et al., 2022, ''The Reference Elevation Model of Antarctica - Mosaics, Version 2'', https://doi.org/10.7910/DVN/EBW8UC, Harvard Dataverse, V1, accessed September 2024.) apart from Latady Island and Charcot Islands which were created from the Copernicus GLO-90 DEM (https://doi.org/10.5270/ESA-c5d3d65). For REMA, the 500m mosaic was downloaded and converted to EGM2008 geoid, and contours were extracted. For the Copernicus GLO-90 DEM, the 90m tiles were used and contours were extracted from these, and then smoothed using a 60m smoothing tolerance. The two areas were merged together, and there is a field in the attribute table called 'source' which details which source each line comes from. The main field is called 'Contour' and contains the height in metres of each contour line. There are also fields for 'surface' which states whether the contour falls on ice or ice-free ground, and a field called 'interval' which states 'yes' or 'no' depending on whether the contour is an interval of 1000 or not. These fields are to improve cartographic presentation of the data, when styled using the fields. The coordinate reference system of the data is WGS84 Antarctic Polar Stereographic, EPSG 3031.

Spot heights:

This file contains 905 spot heights for the Alexander Island region, each point identified as a local high point with the height extracted from the 2 metre mosaic tiles of REMA v2 (Howat, Ian, et al., 2022, ''The Reference Elevation Model of Antarctica - Mosaics, Version 2'', https://doi.org/10.7910/DVN/EBW8UC, Harvard Dataverse, V1, accessed September 2024.) Detailed methodology is given below. All processing was carried out in ArcGIS Pro version 3.3.0, apart from step 2 which was carried out in QGIS version 3.34.7. Only a selection of these heights are shown on the published Alexander Island map, but all of the points that were produced are published here.

1. 32 metre version tiles of REMA v2 were downloaded, merged together, and converted to use Mean Sea Level / EGM2008 heights. The 32 m version was used to start with because the 2 m version was too power and time intensive for processing.

2. Using the 'Spot Height Extractor' Plugin in QGIS (version 1.1 - https://plugins.qgis.org/plugins/Spot-Height-Extractor-Plugin-main/ ), spot heights were extracted from the 32 m mosaic. This plugin identifies local high points. A neighbourhood size of 101 was used, which gave an optimal number of output points.

3. Manual tidying of the output file was performed to delete points on ice shelves, and in other locations ...(72)

Data collection:

ArcGIS Pro (version 3.3.0)

QGIS (version 3.34.7)

QGIS Spot Height Extractor plugin version 1.1

Data quality:

All data is subject to error and known potential errors have been detailed in the lineage statements. Elevation data accuracy statements can be seen in the source data publications. The coastline, rock and lakes have been interpreted from satellite imagery using the dataset creator's best knowledge of the region and available data.