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