In-Class Exercise 4 [Georeferencing]

A. Georeference using historical coordinates (USS Edith, Lompoc)

B. Georeference using geographic features (Bodega Head)

Introduction:Georeferencing existing map data

This week we will focus on the input of digital data. There are a variety of imagery and scanned map sources available on the web and in libraries worldwide. In fact georeferencing scans of historical maps in archives is such a large task some institutions crowd-sourced the effort, for example the British Library georeferenced 3,221 maps Links to an external site.with volunteers online using Georeferencer.com.

Local map collector David Rumsey also has Georeferencer on his website and we'll look at these resources later. 19th century historical maps are useful in Bay Area archaeology because they identify many cultural features that may be covered over today. A series of high resolution topographic maps were created starting in the late 1850s and going forward by the US Coast Survey known as "T-Sheets" Links to an external site.. More background and a presentation of important accompanying information such as the surveyor's field notes is available in ARF Monograph 65 by Scott Byram Links to an external site..

The SF Bay Estuary Institute (SFEI Links to an external site.) is interested in T-Sheets because ancient shorelines and ecological areas appear, so SFEI has prepared a technical information booklet about the use of California T-Sheets in GIS Links to an external site..

NOAA has been scanning these maps and reference footprints for many (but not all) of the T-Sheets are available online

NOAA_Historical_Shoreline_Survey_Footprints.zip Links to an external site.

In this exercise we are going to georeference two T-sheets using common methods you will likely encounter elsewhere.

A. Georeference using historical coordinates

We discussed North American Datum 1983 in class and this is actually the third continental datum to emerge in the twentieth century Links to an external site.. The first was 1901 Datum, the second was known as NAD1927. A great deal of cartographic data was produced between 1927 and 1983 and so the conversion "NADCON" a common GIS operation that is nearly invisible in Arcmap as long as the images are identified in their appropriate datum.

Many of the 19th century T-Sheets have had their coordinates updated to NAD27 so in this exercise we are going to georeference a sheet using updated coordinates.

The Georeferencing process Links to an external site.is described in detail in the ArcGIS Help Files.

Download our exercise data from this folder Links to an external site.

and Unzip it into your Documents directory. Open the folder "CoastSurvey_Edith".

This is a map from 1879 showing the shipwreck for the USS Edith from 1849 that was plainly visible on the beach in central California until later storms and sands obscured the wreck.

Right click the map 1879_LompocLanding.jpg and zoom in on the map title and information on the upper left side. Note the red and blue cross-hairs. Red: US Standard Projection 2/14/12 and in Blue: N.A.Datum 1927 FBK1933 check JPL. It appears that an 1879 map had "US Standard Projection" based on the 1901 datum added in 1912. Two decades later F.B.K. added the NAD27 ticks and this work was checked by J.P.L.

We can use the NAD27 ticks to bring this map into a modern reference system.

1. Load the map and a reference layer

Open Arcmap with a Blank Map

At the top of the screen, select: View, and choose Coordinate Systems and choose Geographic > North America > NAD 1927 [Right-click and Add to Favorites] Exercise 4 part1A step 1.png

File > ArcGIS Online... search for "USA Topo"

The result should turn up 3 maps. Choose the third one that reads "LPK" and Add. There will be an error because USA Topo is not in NAD1927 datum. This is OK we're just using it as a reference. Exercise 4 part 1A step 1b.png

Zoom into the central California coast approximately between Monterey Bay and Santa Barbara.

Turn on the Customize > Toolbars > Georeferencing Toolbar Exercise 4 part1A step 1c.png

Add Data > 1879 LompocLanding.jpg with an "Unknown Spatial Reference", click OK.

In the Georef Toolbar choose Fit to Display. Exercise 4 part1A step 1d.png

If your computer is slow turn off the USA Topo layer for now.

In the center of the 1879 map a creek flows into the sea. Zoom in on that spot and note the shipwreck labeled "Edith". Note the tick marks to the right and left of the shipwreck. Exercise 4 part1A step 1e.png

For the optimal georeferencing we're going to use the tick marks surrounding the feature of interest. At the very least we need four ticks. I have prepared a cropped map with the numbers adjacent the ticks to expedite this in class. Generally I print out a reference copy and write the relevant coordinates on the printed map.

Add 1879_LompocLanding_crop.jpg

Georef toolbar Change the Target layer to the Crop layer (by selecting from drop down menu) Exercise 4 part 1A step 1f.png

Georef > Fit to Display

2. Adding Control Points

Using the Z key (magnifier shortcut) zoom way in on the top-left crosshairs by drawing a box around the ticks and the labels. They should fill the screen

On the Georef toolbar use the left most crosshairs tool "Add Control Points" Exercise 4 part1A step 2b.png

Carefully click right in the + crosshair of the NAD 1927 tic (Remember which color is NAD27?) and then immediately Right click and choose "Input DMS" We are west of Greenwich and north of the equator:

120 38 0 W
34 48 0 N

Click OK and the map immediately moves away because you've got Auto Adjust checked. Click the big blue Back to Previous Extent" arrow in the Tools toolbar (near the globe). This is a fast way to zoom back because it's cached. Exercise 4 part1A step 2c.png

Repeat this process for 3 other tics: Z key for magnifier shortcut and draw box to zoom in. Add control point. Type in appropriate coordinates. Zoom back to Previous Extent.

On the right side of the Georef Toolbar click "View Link Table". This shows the coordinate conversion between raster (Image) coordinats and the system you're connecting it to: NAD1927. Note the Residuals columns on the right. Your goal is to minimize the RMS or Residual. From the window you can Save your control points (disk icon) as text file, eliminate the bad ones with a lot of error, and turn off Auto Adjust if you don't want the map moving. Exercise 4 part1A step 2d.png

Most important step: if you're happy with the result go to Georef Toolbar "Update Georeferencing". Exercise 4 part1A step 2e.png

3. Mapping into a Shapefile in NAD1983

You could create a shapefile and put a point or polygon on the shipwreck, or just record the coordinates indicated. This is a good first step for a geophysical survey. However recall you're still in NAD27.

Now zoom back a ways, turn off the uncropped map and turn on the USGS Topo layer so you can see the Edith crop is positioned well on the USGS map. Exercise 4 part1A step 3a.png

Back in File Explorer (Windows) look in the directory next to the Crop.jpg and note that a .jgw file has been created.

Create a shapefile in ArcCatalog tool. Rightclick the 04_data_acquisition and choose New > Shapefile.... Exercise 4 part 1A step 3b.png

Call the file "sites_p". Geometry: Point. Under 'properties' enter the Coordinate System: Geographic > North America > NAD 1983 Exercise 4 part1A step 3c.png

Three Fields:

Title (Text) Length 50
Descrip (Text) Length 255
Source (Text) Length 255

Add this Shapefile to the map. Create a new feature (make sure you are in 'editor') and put a dot on the Edith. Fill in fields appropriately.

While your project is still in NAD1927 you can add a NAD83 Shapefile. These are well-documented projections with a known conversion so Arcmap has no problem overlaying these layers thanks to "On-the-fly Projection" available in ArcMap. Exercise 4 part1A step 3f.png

If your original map and project was in some older system with more error (such as an attempt to reference into US Standard Datum 1901) this would be more complicated and you shouldn't use "On-the-fly projection" to map features.

Exercise 4 part1A step 3g.png

Exercise 4 part1A step 3h.png

B. Georeference using geographic features

In this exercise we will georeference a map visually using distinctive landforms because we do not have the Lat/long gradicule, UTM grid, State Plane, or other modern reference system to use. The features we use depend in on the scale and accuracy of the maps in question. For the map we are working with the Bodega Head is a very distinctive landform but this technique works with discrete locatable places on the landscape today. Examples: railroad crossings of roads or rivers (two linear features meet), the hydrology network more generally, major road junctions, pointy peaks or ridge junctions. Rocky outcrops (coast surveyors draw dangerous rocks in the waterway very carefully).

Can you think of examples of bad features to use for georeferencing?

You should have already downloaded the Bodega Head map from this directory Links to an external site.. It contains a 1863 Map of the Point Reyes and Bodega

Put it in your Documents under 04_In-Class and unzip it

Look inside the folder. Let's make sure you can see the file suffixes on your windows machine. Go to View menu and choose "Show File Extensions".

Note that there's a 20mb JPG file and a small TXT file in the folder.

Open a new tab in your web browser and drag the TXT file into the browser windows so we can look at it.

This is Metadata. Look at the contents .

2. Open a historical map in ArcMap

First let's load a base map to reference
Open a new map in Arcmap File > New... choose Blank Map
Sign into ESRI File > Sign in... using your ESRI username
Add map service from File > ArcGIS Online...
Uncheck "Only search in UC Berkeley GISC"
search for "USGS Topo" note that there's a USGS Topo box with "open" and another that says "Add". Click Open so it opens in a new map in it's native coordinate system.

3. Zoom to Bodega Bay

Click the Find tool (binoculars) in the "Tools" toolbar (should be on)
Click "Locations" tab and choose locator: World Geocode Service (ArcGIS Online)
Search line: Bodega Bay, CA
Click "Bodega Bay, California, United States" and right click on that line
choose "Zoom To"
Close the Find window
Turn on the Georeference Toolbar
- Customize > Toolbars > Check Georeferencing...
- Dock the Georeferencing toolbar to the top of the Arcmap window by dragging the toolbar topbar
Choose 1:250,000 from the Scale drop down in the Main toolbar.
Click the Add Data (Yellow+ icon) browse to the Coast Survey folder and Add the T00883-00-1863.jpg file
See the "Unknown Spatial Reference" window. What is this about?
- Recall in In-Class 01 the Giza.jpg image appeared in the right location in Egypt and the Latitude/Longitude coordinates confirmed it.
- In the Assignment that you turn in for this In-Class exercise briefly explain why this file is "unknown Spatial Reference" what file would put this JPG in the right location?
Click OK
In the Georeferencing toolbar note that the JPG image name appears. In the Georeferencing... menu choose Fit to Window
Georeferencing... Flip or Rotate > Rotate right...
Choose "Georeferencing... Fit to Display"
The map is roughly positioned. Let's make it semi transparent and place georeferencing points: Right click the T00883 layer in the Table of Contents > Properties. Choose the Display tab. Set it 50% transparent and click <Apply> (not OK).
Drag the Layer Properties window off to the side if you can't see the Bay. Is the transparency good or is it too busy to distinguish the layers? Maybe make the scan more opaque -- choose 20% and click Apply. Ok? Click Ok.
Now, using the "add control points" function (in the georeferencing tool bar) you will add multiple points between identifiable features on the historical map to the underlying topo map. Point 1 (historical map) to point 2 (topo map)..repeat, until the coast of the historical map is roughly lined up along the underlying base map.

4. Save your MXD with Relative Paths

Sometimes Arcmap crashes while you're georeferencing so let's save our project.
Save this map MXD file under File > Save As... and navigate to the 04_In-Class folder. Call it "Bodega"

5. Georeference the JPG image and save out the Worldfile

- In the Georeferencing toolbar click the "Add Control Points" tool which is the leftmost tool
- Now, using the "add control points" function (in the georeferencing tool bar) you will add multiple points between identifiable features on the historical map to the underlying topo map. Point 1 (historical map) to point 2 (topo map)..repeat, until the coast of the historical map is roughly lined up along the underlying base map.
- Update the Georeferencing once you are satisfied.
- recall that you want to optimize your georeferencing around your study subject and the edges of the historical map far from your control points may be ignored.

Three Russian structures of Port Rumyantsev mapped in 1863.

The three rectangles of Port Rumyantsev on the beach are your focus.

Some tips:

use the Z key to zoom in and C key to pan. Drop your control points then use the Blue Return to Previous Extent arrow to pop back out.
This can be an iterative process: roughly georeference, update georeferencing, then return and carefully place 5+ new points to improve correspondence between the maps.
Consider the effects of 150 years of erosion and sand bars on the map (the feature east of the port is somewhat ephemeral).
The tidal zone and cliff faces often have ambiguous features.
Typically 4 to 8 control points are adequate. Examine the RMS residual and eliminate control points contributing a great deal of error to your referencing.
Georeferencing historical maps will result in a much higher RMS error than with modern datasets due to the antiquity of the source. Coast Survey maps are nevertheless high quality for their time.

Open the Attribute tool (Editor Toolbar) or the Attribute Table (shown below) and fully attribute each point as you create it. Exercise 4 part1B step3h.png

Produce a map showing Bodega Head on modern USGS Topo layers with the three structures overlaid on top. Include a scale bar and north arrow. File > Export as... PDF and upload the result.