Maps of Disney Survey Markers

This is a supplement to Patty Winter's Disney Benchmarks Page, which locates and describes every reported Disney survey marker.

This page shows the locations of Disney survey markers using dynamic Google Maps and static images. Google Maps can be zoomed. The static images show more detail. Google Maps uses U.S. Geological Survey aerial imagery and other satellite imagery. The static images use U.S. Geological Survey aerial imagery.

The location of each Disney survey marker is indicated by a green Google pushpin or a green circle. The lines of sight between markers are indicated by green lines. The intent is to provide an overall view of where Disney places its survey markers. By looking at the placement of known markers and their lines of sight, it might be possible to deduce the locations of others.

Click the heading links to go to the corresponding section of the Disney Benchmarks Page. Click the preview images or the links below them to go to the maps or enlarged images.

Google Maps requires a recent web browser and javascript.

The static full-size color images are very large. If your web browser cannot display the full-size color images, try the intermediate-size color images.

Maps

Disneyland

It is not known how many survey markers exist at Disneyland. 2 covered survey markers, 4 large survey markers, and 21 small survey markers have been found by the public. (3 of the large survey markers have been destroyed recently.)

Disney World

Disney World reportedly has 70 large survey markers and an unknown number of small survey markers. 57 large survey markers and 6 small survey markers have been found by the public. (1 of the large survey markers has been destroyed recently.)

Euro Disney

No survey markers have been found by the public.

Tokyo Disney

No information has been received about Tokyo Disney.

Hong Kong Disney

Hong Kong Disneyland reportedly has 11 survey markers. No survey markers have been found by the public yet.

Under Review

No survey markers need to be reviewed at this time.

Technicalities

Technically, these are not simply aerial photographs. The grayscale USGS Digital Orthophoto Quadrangles and color USGS Urban Area High Resolution Orthoimagery have been mathematically processed to remove distortion and to have a uniform scale. This makes it possible to measure directly on the images. The scale of the reduced-size preview images displayed here is 4 meters per pixel (about 13 feet per pixel). The full-size grayscale images are 1 meter per pixel (about 3 feet per pixel). The full-size color images are 0.25 meters per pixel (about 10 inches per pixel).

The process of going from GPS coordinates to the images displayed here is longer than you would expect because I tried to be as accurate as possible.

The USGS DOQs and Urban Area orthoimages are based on NAD 83, while GPS is based on WGS 84. GPS receivers treat NAD 83 as if it is identical to WGS 84. These datums are very similar, but they are not identical. The HTDP program can be used to transform positions from WGS 84 (G1150) to NAD 83 (CORS96). Besides the latitude and longitude, you also need to know the ellipsoid height and the epoch dates. The ellipsoid height at a location is the sum of the elevation and the geoid height. The National Map can be queried for the elevation of any point in North and South America. The average elevation of Disneyland is 41 meters (135 feet) and that of Disney World is 30 meters (100 feet). The GEOID99 program can compute the geoid height, which is -35 meters (-115 feet) at Disneyland and -28 meters (-90 feet) at Disney World. In this case, the date the GPS reading was taken is the WGS 84 epoch date and the dates the aerial photos were taken can be used as estimated NAD 83 epoch dates. Using all this information and the INVERS3D program to compute the distance between two points, I calculated that the horizontal differences between WGS 84 and NAD 83 are about 1.5 meters (5 feet) at Disneyland and 0.7 meters (2 feet) at Disney World. Since these discrepancies would be visible on the 0.25 meter color images, I converted all GPS coordinates with HTDP before using them.

USGS DOQs and Urban Area orthoimages are publicly available through TerraServer USA (not to be confused with the commercial TerraServer). USGS Urban Area imagery has a resolution of only 0.3-0.65 meters, but TerraServer USA resampled it to 0.25 meters to fit in better with the 1 meter DOQs. The TerraServer USA Geographic Coordinate Search does not zoom in on exact latitude and longitude coordinates, so I used my own interface to retrieve images through their Sample Map Server. The grayscale aerial photos for Disneyland were taken in 1995 and those for Disney World were taken in 1999. The most obvious differences are that the Disneyland imagery shows the old parking lot instead of the new California Adventure and that the Epcot imagery shows the old Horizons Pavilion instead of the new Mission: Space Pavilion. The color aerial photos for Disneyland and Disney World were taken in 2004 and 2002. Unfortunately, the USGS Urban Area coverage ends right in the middle of Disney World. It includes Magic Kingdom and Epcot, but does not include MGM Studios and Animal Kingdom.

I retrieved 500 x 500 meter images surrounding each survey marker. By using the Map Server crosshair grid lines, I plotted the GPS coordinates (the centers of the circles) to the corresponding pixel. Of course, ordinary GPS receivers are not anywhere near that accurate. Magellan and Garmin both cite a typical GPS accuracy of 15 meters (~50 feet) 95% of the time. Therefore, I drew each circle with a radius of 15 meters. I chose to color the circles green without altering the luminance. This method preserves the grayscale detail in the original imagery, but it doesn't work well in black areas and white areas. It's also difficult to distinguish individual circles when the markers are close to each other. I then merged the separate 0.5 x 0.5 km images to create the resulting composite images. Finally, I drew green lines connecting markers where lines of sight exist.

Even if a GPS reading happened to be perfect, there is more unavoidable error in this whole process than you might realize. GPS coordinates in the decimal minute format have only 3 decimal places so they are precise to only ±0.9 meters. The precision of the Map Server grid lines is not known, but they have been observed to vary in the range of ±3 pixels (±3 meters for DOQs and ±0.75 meters for Urban Areas). Assuming that TerraServer USA aligns the imagery correctly, there is still some error in the imagery. The USGS reports root mean square errors of 0.8-1.7 meters for the appropriate DOQs and 0.7 meters for Urban Areas. Loosely translated, the error should be within ±3.0 meters 95% of the time for DOQs and ±1.2 meters 95% of the time for Urban Areas. Adding all this up, the total error in plotting a perfect GPS reading is about ±6.9 meters (23 feet) on DOQs and ±2.9 meters (9 feet) on Urban Areas.

However, even with possible GPS inaccuracies of 15 meters (~50 feet) and possible plotting errors of 7 meters (23 feet), it isn't that bad in practice. When the plotted locations of the survey markers were compared to the actual photographed locations of the survey markers, the empirical error was found to be much smaller than the green circles. The majority of the plotted locations appear to be within 3 meters (10 feet) of the actual locations. Of the locations where the error could be estimated and measured, the RMS error is 3.9 meters (13 feet). All plotted locations are within 12 meters (38 feet).

All USGS DOQs and Urban Area orthoimages are in the public domain.

Google Maps has additional Terms of Service.

Please send any comments or corrections regarding this page to Lloyd Lee-Lim <ltleelim@mail.limunltd.com>.

 

Disney Survey Markers / 26 Jan 2006