Shorelines and Bluff lines for 1938, 1980, 2009 and 2016 were digitized along the Great Lakes coastlines of the State of Michigan. The Lake Michigan coastline of Michigan's lower peninsula was completed in 2017 (Berrien County only) and 2018 (northern extent of Berrien County to the northern extent of Mason County).

Aerial photography from 1938, 1980, 2009 and 2016 were acquired in digital format, georeferenced to its correct location on earth, and used as the base layer to digitize shoreline and bluff features.

Aerial imagery for years 2016 and 2009 were acquired from the USDA National Aerial Imagery Program (NAIP). Imagery for 1980 and 1938 were acquired from the Michigan Department of Natural Resources (MDNR) Office of the Great Lakes (OGL), or the Michigan State University (MSU) Historical Aerial Imagery Archive.

NAIP imagery for 2016 and 2009 is already georeferenced by the USDA, but OGL and MSU imagery imagery for years 1980 and 1938 were manually georeferenced using ArcGIS Desktop 10.6 software and 2016 NAIP imagery as the base layer that historic images are aligned to.

Accuracy statements for 2016 NAIP imagery were evaluated and 2016 NAIP imagery was compared to published NOAA Raster Navigational Charts for areas along the lakeshore in Berrien County, MI. Shoreline features such as breakwalls and piers, digitized using 2016 NAIP imagery, aligned very closely with the same features on the Raster Navigational Charts. This supported the decision to use 2016 USDA NAIP imagery as the base layer to georeference previous years of imagery to.

Image mosaics were created for geographic groups along the shoreline and analysts focused their efforts on one of these groups at a time.

Shorelines, defined as the 'landward extent of wetted sand or beach material', were digitized by analysts using the georeferenced imagery. Shorelines for 2016, 2009, and 1980 were digitized at 1:1,000 scale or better, while 1938 shorelines were typically digitized at 1:3,000 scale. Shoreline and bluff-line features for each year should align with their respective georeferenced imagery when viewed at the digitizing scale.

Blufflines, defined as the 'lakeward-most edge of relatively level ground that breaks or drops off abruptly, usually characterized by loss of vegetation', were digitized using the same techniques as those used for shorelines. 1-Meter Digital Elevation Model data was procured for coastal areas of Michigan where it is available to help identify modern-day bluff locations (most new DEM data is from 2015 - 2017). Topographic contours were generated and used as an analysis overlay during bluff digitization work.

When linework for a country is completed it is reviewed by another team analyst. Analysts worked together to resolve inconsistencies in interpretation or identification of other issues such as error in georeferencing.