Mapping Alaska’s Mat-Su Basin

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Why We Love It

You don't have to look at the legend to understand what this map conveys. It depicts 28,000 miles of previously unmapped waterways and critical habitat in South Central Alaska’s Matanuska-Susitna (Mat-Su) Basin. Using greyscale and opacity to mask everything outside the study area, the map provides a clear delineation of the watershed boundaries. In contrast, vibrant colours within the basin successfully draw the reader in and keep the focus on the intended theme of the map.

Why It Works

The Matanuska-Susitna Basin has a complex geography and dense hydrologic network of streams, rivers, and lakes. This map works by employing important techniques to present a striking view of the entire area. The map author uses colour masterfully to highlight and accentuate the most important elements. Additionally, only the most critical labels are provided for reference. As an observer, we get a clear and unimpeded representation of the Mat-Su Basin and its conglomerate of hydrologic features.

Important Steps

Conduct a high-resolution (1:24K) update to the USGS National Hydrologic Dataset. Choose symbology for linear stream and areal lakes. Download the USGS Mat-su NHD report here to learn how to do this.

Use image analysis window to clip glaciers out of the Digital Elevation Model, then assign a custom cyan colour ramp to the clipped glacial elevations.

Create an Elevation legend which corresponds with colour tinted shaded relief.

Use NOAA bathymetric Digital Elevation Models to depict ocean depths.

Use Esri S-57 viewer for depicting coastlines and bathymetric contours with NOAA Electronic Navigational Charts.

Make the area of interest “pop” with a greyscale background. The greyscale basemap is not a hillshade. Rather, it is a 90 m DEM shaded relief created with the image analysis window assigned with greyscale colour ramp under the Esri Light Grey Canvas basemap with 50 percent transparency applied.

Requirements

Data

Datasets include the USGS NHD and NED, local LiDAR and IfSAR elevation data (conflated to the NED), transportation, annotation and boundary layers published by the Mat-Su Borough and City of Anchorage, US Census data, and NOAA ENCs and bathymetric DEMs. TNC Alaska Science Director David Albert provided valuable cartographic advice.

Analysis

Primary analysis is the 2015 update to the USGS National Hydrographic Dataset which used the “ele-hydro” concept of elevation-derived flowline modelling to build the 53,000 lineal mile hydrologic network represented on the map.

Time

This map went through many iterations from 2014 to present. By the time it entered the 2016 Esri UC Map Gallery, roughly 400 hours had been spent on it.

Raster Datasets

Tips

When using raster datasets for cartographic purposes, rely heavily on the image analysis window and raster functions to hold data in memory rather than create new files.

Varied Topography

Tips

It can be difficult to find a single color ramp to highlight varied topography such as flat valley floors and steep mountainous areas in the same DEM. However, you can clip and mask portions of the DEM to assign individual color ramps to different topographic “categories” so no details are lost.

AOI

Tips

For areas of interest, which include an interface between terrestrial and Marine/Ocean areas, NOAA ENCs have a range of interesting symbology that can add character to the transition between bathymetric DEMs and elevation DEMs.

More Information

Map Author

Jim DePasquale

Jim DePasquale

Jim is a spatial analyst with the Alaska Chapter of The Nature Conservancy.

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