By: Bob Cowling
The American Geographic Society Library (AGSL) in Milwaukee, Wisconsin, houses a large collection of international nautical charts ranging from the 19th to the early 20th century. In 2015 a grant-funded project was started at the AGSL to digitize and catalog around 5,500 international nautical charts. As of 2021, the project is still ongoing with about 2,200 nautical charts scanned and available online. In fall 2020, an interactive web mapping application called the AGSL Nautical Chart Explorer was developed to serve as an online discovery aid for this collection of rare nautical charts from around the world. The primary goal of the Nautical Chart Explorer is to allow the user to be able to view high-resolution images of the scanned nautical charts directly in the application. The application is an index map, which gives users the ability to find nautical charts by geographic location. Users can select and view a specific series of historical nautical charts in the AGSL collections. Upon clicking on the bounding box of any chart, the application provides the user with metadata, as well as a high-resolution image corresponding to each chart in the series. The project is an early use case of the OpenIndexMaps schema. This application is useful for researchers and students, but the primary audience is the general public. This article will explain the purpose of the nautical chart application, the information available in it, the application’s various features, and challenges that were encountered when developing an application of this nature.
When using the application, there is the option to select a chart series. At this point in time, there are five international chart series available to choose from: British, Dutch, French, German, and Russian. The application will be expanded to include more chart series for different countries in the near future.
Upon selecting a chart series, the map will update with a series of orange bounding boxes, which represent the geographic extent of each scanned map in the series. When the user clicks on one of these boxes, a pop-up window will be displayed providing a thumbnail of the scanned map and various metadata fields such as Title, Author, Year, Publisher, and a link to the item in the library catalog.
The application offers the feature of allowing the user to view the scanned nautical chart in super high resolution using the ‘view image’ button in the pop-up. The view image button launches a pop-up window with a tiled-map image that can be zoomed in and out of at different locations on the map.
Search functionality is offered within the application as well. The user can type the title of a chart into the search bar and select it from results that are auto suggested. The map will then zoom into that specific chart and open a pop-up displaying the corresponding metadata information.
The nautical charts explorer provides users with the ability to download data for a specified chart series in either CSV or GeoJSON format with the simple click of a button. Choosing to download a CSV will produce a spreadsheet with the metadata for all charts in the selected series. Choosing the GeoJSON option will download the selected chart series with the corresponding metadata as well as the geometries for the bounding boxes of each chart. The GeoJSON file can then be imported into desktop GIS software or used on any web mapping platform.
When building an application of this nature, the biggest challenge was making it user friendly. Building an index map with over 2,000 features can be challenging because there are many overlapping indices creating a significant amount of screen clutter, which can be overwhelming or confusing to the user. Overlapping indices were inevitable, but in an effort to reduce clutter, the user can only select to view one chart series at a time. Also, as the user zooms into the map, the bounding boxes of the smaller scale charts begin to disappear, with only the charts with a larger scale remaining visible.
The AGSL Nautical Chart Explorer was designed as a discovery tool to allow users to find historical nautical charts. This project is still ongoing, and as more nautical charts are scanned a cataloged, they will be added to the application. To view the map and explore nautical charts in the AGSL collections, please go to the AGSL Nautical Chart Explorer website.
MLIS Student – University of Wisconsin-Milwaukee
Master of Science in GIS & Cartography – University of Wisconsin-Madison