Bringing Historic Maps into GIS Patrick Florance Digital Cartographer Harvard Map Collection Harvard University
Purpose • Demonstrate how historical maps can be used within a GIS. • Illustrate the techniques used to bring historical maps into GIS • Show types of maps that are useful to bring into GIS • Convey research conducted at the Harvard Map Collection
GIS • A geographic information system (GIS) is a configuration of computer hardware, software, and personnel specifically designed for the acquisition, maintenance, and use of geographically referenced data. • Modification of Dana Tomlin’s definition Geographic Information Systems and Cartographic Modeling (1990)
Why bring historic maps into GIS? • Use historic maps within GIS as a tool for understanding the spatial relationships of past phenomena • Deforestation • Shoreline change • Socio-economic characteristics of a state or a neighborhood • Place-names • Railroads and transportation networks • Disease
Why bring historic maps into GIS? • Context: What exists within one’s study area at a given point(s) in time? • Overlay modern GIS data over historic maps • Early 20th century USGS topographic map of central Mass.
Why bring historic maps into GIS? • Context: What exists within one’s study area at a given point(s) in time? • Overlay modern GIS data over historic maps • Early 20th century USGS topographic map of central Mass. • Overlay modern Quabbin Reservoir in semi-transparent blue
Why bring historic maps into GIS? • Context: What exists within one’s study area at a given point(s) in time? Close up of northern Quabbin over early USGS topographic map. Features flooded:Towns, roads, railroads, etc.
Why bring historic maps into GIS? • Feature Extraction (heads-up digitizing) and encoding • Vectorize: discrete data made up of ordered lists of points and represented by points, lines, and polygons • Trace features and encode those graphics with information • Surface of the earth • Anthropogenic features • Places, place-names, roads, railways, trails, buildings, bridges, etc. • Natural features • Rivers, lakes, shoreline, elevation, etc. • Abstract/Administrative geography • Country, state/province, municipal, parcel/property boundaries, census tracts, etc.
Why bring historic maps into GIS? • Feature Extraction (vectorization) • 1898 USGS topographic map of Portland, Maine
Why bring historic maps into GIS? • Feature Extraction (vectorization) • 1898 USGS topographic map of Portland, Maine • Built area extracted (vectorized) in red. • Perhaps trace roads, railroads, shoreline, contours, etc. • Note edge.
Why bring historic maps into GIS? • Resource/Research Management Tool • More and more researchers using spreadsheets to manage their research to collect information about places and source material • Think of GIS as sort of a spatial spreadsheet or database, which can be used to join that information to spatial representations
Why bring historic maps into GIS? • Analysis • Simple • Finding inns that are located within 5 miles of towns with a population over 10,000 in southern France around 1910. • More complex • Archaeological predictive modeling • Spatial analysis techniques to model fire density or disease patterns
Why bring historic maps into GIS? • Analysis Interpolated fire density of Constantinople, 1660.
Why bring historic maps into GIS? • Graphic presentations or visualization • Make maps, charts, graphs, etc. • Very powerful and useful • See David Rumsey Example
Historic Map as a GIS Data Source • Historic maps are made for communicating, not for serving as a basemap/source data for a modern GIS. • Positional accuracy: features often moved slightly for clarity (i.e., clustered places, roads along rivers, etc.) • Scale distortion • Edge-matching • Insets • Paper streets • 1890 map vs. 1990 map
Data Conversion/Development Process • Convert maps to digital form • Georeference the digital maps: assign them meaningful spatial coordinates • Feature extraction and data modeling ($$) • Generally around 80% of project cost • Heavy overhead before one gets results, which is one of reasons why so many GIS fail.
Convert Printed Map to Digital Image • Digital Image (Raster) is composed of a grid of pixels 1898 U.S. railroad map
Convert Printed Map to Digital ImageEquipment • Large-format scanner • Expensive • Scarce • Overhead digital photography • Be careful using photocopies • Distortion along edges
Convert Printed Map to Digital ImageResolution • Resolution can be expressed as the number of pixels per inch (PPI) • Different from spatial resolution of remotely sensed imagery, which is a measure of the smallest object that can be resolved by the sensor or the dimension on the ground represented by each pixel (i.e., 30 meters)
Convert Printed Map to Digital ImageResolution (Cont.) • Generally between 150 - 600 ppi, average 200 - 300 ppi • Determine resolution that captures the smallest significant feature • Use consistent resolution if working with a map series • Capture uncompressed as TIFF (Tagged Image File Format) • Consider using image compression for working file • If map is in grayscale, capture it in grayscale color model • reduce file size • If map repository, consider capturing very high quality for archiving & resampling to lower resolution for GIS work
Georeference the Digital Image/Map • Georeferencing converts a digital image (raster dataset) from a nonreal-world coordinate system (image space) to a real-world coordinate system such as latitude and longitude. • Makes it “line up” with other GIS data. • Allows the digital map image to be viewed with other GIS data.
Georeferencing Process • Need to know locations of at least 3 recognizable features • Use more than 3 • Locations used to create control points • Spread out throughout the map 1898 U.S. railroad map
Lat/Long Lat/Long Lat/Long Georeferencing Process • Need to know locations of at least 3 recognizable features • Use more than 3 • Locations used to create control points • Spread out throughout the map • Link real-world coordinates to the control points • Links used to transform the map image to real-world coordinates
Georeferencing: Transformation • Transformation adjusts the digital map to make it fit in this real-world coordinate system • Affine Transformation - most common • Scale • Skew • Rotation • Shift (Translation)
Affine Transformation: Scale • Changes the image scale by expanding or reducing
Affine Transformation: Skew Before After X Y
Affine Transformation: Rotation • Rotates x and y axes so that the image is correctly oriented Before After X Y
Affine Transformation: Shift (Translation) • X and Y origin are shifted Before After X Y
Georeferencing: Transformation Complete • Software creates associated files that contain the coordinate information (i.e., .tfw) • Digital map can then integrated with other GIS data 1898 railroad map with modern vector shoreline overlaid
Root Mean Square (RMS) error • Root Mean Square (RMS) error • Describes the deviation between the control points in the output image and the values calculated by the transformation • A measure of the accuracy of the control points • In general, lower number the better, with 0 being perfect • Record RMS error • Save control points
Georeferencing Techniques forHistoric Maps • Use existing coordinates or tics • Link features on map to features within GIS datasets that have known real-world coordinates. • Global Positioning System (GPS)
Use Existing Coordinates or Tics to Reference the Map in Real-World Coordinates Over 134 types of features: towns, municipal boundaries, road types, railways, hydrology, rice fields, pasture land, post offices, churches, castles, inns, etc. Austro-Hungarian Monarchy Topographic Series, Scale: 1:75,000; Date: 1874-1912
Use Existing Coordinates or Tics to Reference the Map in Real-World Coordinates Topographic map misaligned with modern GIS municipal boundaries (red)
Use Existing Coordinates or Tics to Reference the Map in Real-World Coordinates • Step 1: map research • Map projection: polyhedric projection (antiquated) • Coordinate system: Bessel 1841 spheroid • Spheroid: estimated shape of the earth as a sphere • Prime meridian: Ferro • Metadata is often located on the topographic map itself • However, not in this case • Significant role for the historian
Use Existing Coordinates or Tics to Reference the Map in Real-World Coordinates • Step 2: Create a point layer • From geographic coordinates of the 4 corners • Based on the historic coordinate system (Bessel 1841) and prime meridian (Ferro)
Use Existing Coordinates or Tics to Reference the Map in Real-World Coordinates • Step 3: Project points into the historic map projection • Polyhedric antiquated • Used a polyconic
Use Existing Coordinates or Tics to Reference the Map in Real-World Coordinates • Step 4: Link tic marks on the map to the projected corner points.
Use Existing Coordinates or Tics to Reference the Map in Real-World Coordinates • Step 5: Transform the map Georeferenced topo with modern GIS municipal boundaries and rivers overlaid
Use Existing Coordinates or Tics to Reference the Map in Real-World Coordinates Close up: modern municipal boundaries (gemeinden) overlaid on topo • Disparate datasets never match up perfectly • Off by around 300-400 feet • Detail on map: churches, road types, pastures, etc.
Mosaic: Match Adjoining Map Sheets • Image processing software • Adobe Photoshop • ERDAS Imagine • ArcGIS Spatial Analyst • Time consuming
Other Useful Maps with Coordinate Systems • Topographic series • USGS 1890s – 1950s: 1:62500 • England & Wales: 1805-1874, 1:63,360 • German Karte des Deutschen Reiches: 1862-1907; 1:100,000 • China Ministry of National Defense Land Survey: 1901-1947; 1:100,000 • Survey of India: 1866-1910; 1:253,440. • Nautical charts • Shorelines, soundings, etc. • World and regional maps • Historic places, national and provincial boundaries, transportation networks, etc. • Globes
Georeferencing Techniques forHistoric Maps • Use existing coordinates or tics • Link features on map to features within GIS datasets that have known real-world coordinates • Global Positioning System (GPS)
Feature Linking Use control points to link features on the map to features within a GIS dataset that have known real-world coordinates 2001 MassGIS Digital Orthophoto 1797 Street Map of Boston
Feature Linking Steps • Acquire GIS reference dataset to link the map to • Should be of equal or slightly better scale • Map research • Map projection, coordinate system/datum • Identify additional map sources for reference • Establish reference points to use as links • Cultural features such as street intersections, bridges, buildings, landmarks, monuments, etc. • Try to avoid using natural features such as shoreline, rivers, lakes, etc. because they fluctuate greatly • Check dates of features on the map used as links • Project GIS data to match the projection of the map
Feature Linking Steps (Cont.) • If georeferencing multiple maps, start with the most current map and work backwards in time • Provides more features to link to 1797 1835 1895 2001
Feature Linking Steps (Cont.) • Add at least 3 control points spread out throughout the map • Transform the map 2001 MassGIS Digital Orthophoto 1797 Street Map of Boston
City-Wide Maps: Boston • Useful for tracing the historical development of: • Streets • Districts & wards • Shoreline • Town boundaries • Monuments • Churches • Schools • Significant buildings 1797 - 2001 shoreline change
City-Wide Maps: Cambridge Full View 1865 street map of the City of Cambridge, MA