Martyn Keen




Recently I  completed digitising the 1921 Map of Corregidor Island Military Installations.

Although I refer to it as if it were a single map, those who are familiar with it will recall that it is not actually one single map, but a set of eight smaller adjoining and overlapping maps detailing separate portions of the island. These are available as scanned originals from the Map Room, numbered D1 to D8; and originally titled Manila Bay, P.I.; Fort Mills; Corregidor Island.

The purpose of digitising this map was basically personal. I wanted a map to reference snapshots of existing Corregidor features and for use as a form of navigation to other less frequented sites. Being the clearest maps readily available, I had tried cutting up and joining the 1921 Edition, but the results were a bit disappointing. So, I decided to try to digitise the maps instead.

To do the digitising I used a Geographical Information System (G.I.S.) program to complete drafting; two digital photograph processing programs to manipulate scanned maps; and a Portable Document Format (PDF) program to print the final product.

How did I produce the digital map? First step was to digitally join the 1921 Maps D1 to D8 in Corel PHOTO- PAINT. The JPG format scans were joined relatively easily, except for map D8 of the Wheeler and Searchlight Points area. This latter map appeared to be stretched along its western boundary to the north-west and south-west (sort of trapezoidal shape).

 The next step involved confirming the digitally joined maps conformed to the outline of Corregidor Island. Luckily, there is a General Map with the August 12, 1921 series and the 1941 Emergency Map to help complete this task. The confirmation was done in Adobe Photoshop, a program which allows layering and manipulation of various digital images. Each layer can be transparent to allow overlapping detail from all layers to be compared.

The third step involved entering available geographic information into G.I.S. and onto Zone 51P, as UTM eastings and northings (Universal Traverse Mercator positions in metres). This information included known G.P.S. coordinates of features on Corregidor and coordinates from other sources. This information ensured that any produced map would be geographically positioned.

Now the big test the fourth step, placing the digitally joined map file as a G.I.S. reference image, positioned within the geographical monuments. Guess what? The joined maps fitted close enough to consider digitally capturing the visible features on the 1921 Map.

The next step was digitally placing shapes, lines and line stream combinations over the various feature displayed on the reference image. A different G.I.S. layer was used for each feature group such as: all buildings are on layer 1, coastline on layer 2, contour interval on layer 17 and all roads are on layer 41. This makes digitising easier (digitising all features of one group first and then turning the completed layer off to clear the computer screen) and allows separate and/or combined layer printing.

The digitising is fairly straight forward. Digitising over a reference image is similar to tracing except that the operator can zoom on the reference image for accurate placements of line work. Another advantage is that any number of reference images can be added to G.I.S to confirm detail or add additional detail. During this step a number of C.H.S. members assisted with additional detail and were kind enough to edit and comment on the draft product.

The second last step is to print the final map. This can be done on a plan printer on various large sized sheets of paper or as a PDF file for electronic distribution. Being digital the 1921 map can also be divided into and printed in the original multiple sheets format.

Sample Section of the Digital Map

The last step is is now done. The digital map bas been be proofread by a team, corrected, updated and improved as required.

The map is a faithful reproduction of the 1921 map as a single map sheet. It has the period abbreviation, battery, building, symbol and structure legends as the original. Being a digital file, it can be enlarged or reduced to any scale required.

A copy of the single page map, in Adobe Acrobat format, will now form a part of the "Membership bonus" for new & renewing members of the Society and the 503d PRCT Heritage Bn.

My next project is the 1935 map and then the large sheet 1936 map. Both of these are approaching the proofreading stages.


Martyn Keen

4The  predominant activity of the CHS is the publication of the Corregidor Then and Now Website.