Weddell seal reporting grid of the Vestfold Hills, Antarctica

This is a digital version of the grid reference map used to plot all sightings of Weddell seals in the Vestfold Hills. The point of origin is the same as the original map and each grid cell is numbered with the same numbering scheme. This can be used to plot any data using the same numbering scheme by joining (ArcInfo) or linking (ArcView) records to this coverage's polygon attribute table (pat) through the item GRIDREF.

The original map was a 1:100 000 map of the Vestfolds, provided by Harry Burton, with a grid drawn over it. The grid references were given as either six or four figure values on which field scientists are to plot their data.

This map has the following Antarctic Division drawing reference number:

M/75/05A

Some research with John Cox revealed that this grid was drawn up over a map digitised from another map with the following specifications:

Scale 1: 100 000
Date: 1958 (reprinted 1972)
Projection: Polyconic
Published by: Division of National Mapping, Canberra
Reference number: NMP/58/084

Data are referenced to a 'grid' of 1 minute spacing in x axis and 30 second spacing in y axis. The point of origin is apparently 68 20 S 77 48 E. There are 45 rows and 47 columns.

The 'grid reference' is in fact in geographic coordinates (but using arbitrary units) so the projection of the original map became irrelevant.

The procedure adopted to create a new digital grid was as follows:

(Carried out in Arc/Info)

1. Generate a coverage using the original 'grid references'.
2. Tics were also generated using the corners of the 'grid reference' system.
3. A new coverage was created with tics at the same locations but given the true latitude/longitude vales.
4. The original coverage was then transformed to the new coverage based on the new tic values.
5. The new coverage was then projected from geographic coordinates to UTM metres.

The data locations were then viewed in Arc/Info using a coverage of the coastline supplied by the Mapping Officer, Antarctic Division. This had previously been determined to be in the UTM projection.

An offset was clearly visible between the data locations and the coastline. In order to determine whether the offset was more or less uniform, ten locations were plotted from the original data onto the original map using the 'grid'. Finally a manual corrected was made by moving all the data locations by a uniform distance of 508 metres north and 68 metres west.

Information from John van den Hoff, February 2019:
The grid cells were originally labelled from 1 to 47 along the x axis and 1 to 45 along the y axis. The four digit values in the GRIDREF field of the attribute table are the x value followed by the y value.
To avoid confusion between x and y values, the grid was later revised so that the y values were prefixed with a ‘1’ so for example 01 became 101. The GRIDREF_X and GRIDREF_Y fields have the x and y values of the revised grid.
This needs to be kept in mind when data is sourced from field books.
The map shows the revised grid.

本数据集为用于标注韦斯特福尔丘陵（Vestfold Hills）内所有韦德尔氏海豹（Weddell seal）目击记录的格网参考地图数字化版本。其原点与原始地图一致，且每个格网单元采用与原地图相同的编号规则进行编号。通过将记录通过GRIDREF字段关联至本要素集的多边形属性表（pat），即可使用该编号规则标注任意同类数据，该操作可在ArcInfo中通过连接实现，或在ArcView中通过链接实现。

原始地图为哈利·伯顿（Harry Burton）提供的比例尺1:100000的韦斯特福尔地区地图，其上叠加了格网。格网参考值分为六位或四位数字格式，野外科研人员可据此标注其观测数据。

该地图的南极部门绘图参考编号为：M/75/05A

与约翰·考克斯（John Cox）的相关研究表明，本格网叠加自另一幅经数字化处理的地图，该原始地图参数如下：
比例尺：1:100000
制作年份：1958年（1972年重印）
投影方式：多圆锥投影（Polyconic）
出版方：堪培拉国家测绘局（Division of National Mapping）
参考编号：NMP/58/084

数据所参考的格网在X轴方向间隔为1角分，Y轴方向间隔为30角秒。其原点坐标为南纬68°20′、东经77°48′。该格网共包含45行与47列。

本“格网参考”实则采用地理坐标系（但使用任意单位），因此原始地图的投影方式不再具有意义。

新建数字化格网的操作流程如下（均在ArcInfo中完成）：
1. 基于原始“格网参考值”生成要素集（coverage）
2. 基于“格网参考系统”的四个角点生成控制点
3. 新建一个要素集，其控制点位置与原要素集一致，但赋予真实的经纬度坐标值
4. 基于新控制点的坐标值，将原始要素集转换至新坐标系下
5. 将新要素集从地理坐标系投影至UTM米制坐标系

随后，借助南极部门测绘官员提供的海岸线要素集，可在ArcInfo中查看数据点位。该海岸线要素集此前已确定采用UTM投影。

数据点位与海岸线之间存在明显偏移。为判断该偏移是否大致均匀，研究人员利用“格网”将10个原始数据点位标注至原始地图上。最终通过手动校正，将所有数据点位统一向北偏移508米、向西偏移68米。

2019年2月约翰·范登霍夫（John van den Hoff）提供的补充信息：
格网单元最初沿X轴按1至47编号，沿Y轴按1至45编号。属性表中GRIDREF字段的四位数字值依次为X轴编号与Y轴编号。
为避免X、Y轴编号混淆，后续对格网进行了修订：将Y轴编号前添加前缀“1”，例如原编号01变为101。属性表中的GRIDREF_X与GRIDREF_Y字段分别存储修订后格网的X、Y轴编号。
在从野外记录本调取数据时，需注意该修订规则。本数据集附带的地图展示的为修订后的格网。