README.MAP 6.8b               ALL ABOUT MAPS


NOTE: The file MOREMAPS.txt has a list of state APRS map coordinators and
information on obtaining other APRS maps not in standard distribution.
Serious map makers should read suggestions in MOREMAPS.txt and CDROM.txt.

OVERVIEW:  My general philosophy is to keep maps simple so that APRS will run
quickly on any PC machine, including 8088 laptops, and so that maps can be
made by anyone and distributed within the amateur community without any
license or royalty concerns.  To avoid licensing concerns, I finally decided
to do my own graphs that anyone could use and understand.  For these reasons,
APRS limits the number of points to 2999 and the number of labels to 199; any
more detail on one map just clutters the screen.  This does NOT limit overall
map resolution, however, since APRS overlays maps of increasing resolution as
you zoom in.  To see the street level ability of APRS, Zoom in to the 1 mile
range in the center of Idaho Falls, Idaho.

MAPS DISTRIBUTION:  As of Feb 95, APRS is now being distributed in an East
and a West USA version.  See sections in this file on MAPLIST.xxx, MAP
HEIRARCHY, and ADDING MAPS to understand how the following MAPLIST files
control the way APRS accesses maps.:

MAPLIST.USA  -  Default APRS maplist
MAPLIST.Eas  -  Favors the East  {same as USA plus some smaller E.coast maps
MAPLIST.Wes  -  Favors the West      "                          W.
MAPLIST.cen  -  Favors Central       "                          Central
MAPLIST.SE   -  Favors S.East        "                          S.east

MAPLIST.AK   -  Unique maps for Alaska      { These maps are NOT integrated
MAPLIST.CA   -  Unique maps for California  { into the above .APR files,
MAPLIST.MI   -  Unique maps for Michigan    { since they can be loaded on
MAPLIST.MN   -  Unique maps for Minnesota   { the fly using the FILES-CHANGE
MAPLIST.MO   -  Unique maps for Missouri    { command.
MAPLIST.OH   -  Unique maps for Ohio

MAP COMMANDS:  Before getting into the detail of building APRS maps, use
some of the MAP-MENU commands in APRS to become familiar with the APRS map
structure.  You will see how maps are overlayed in a hierarchical manner
from the whole world, down to increasing detail.  This hierarchical order is
established in the sequence of maps in the MAPLIST.xxx file which tells APRS
the names of all the maps available to it, their size, and the location of
their center.  APRS compares the location of the cursor relative to this list
to decide when to load a new map.  The following MAP-MENU commands will help
you see this hierarchical structure:

  B - Borders:  Shows borders of all MAPS in the MAPLIST.xxx file.  To see
      more and more borders, use the F3 key to soom into further detail.
      If a map border appears, but the map does not come up in APRS, then the
      MAP file is missing.  If the Map file exists but the borders do not show
      up, then the file is not listed in the MAPLIST.xxx file.  See F-C below.

  H - Hierarchy:  This is an improvement on the BORDERS command since it
      colors in the maps in the same sequence as they are listed in the
      MAPLIST.xxx file.  The overlapping colors show the effect of the
      sequence of this list. If you see any border that is not colored in with
      its own color, then it will be invisible to APRS, since it is overlapped
      by other maps of the same area following it in the MAPLIST.xxx file.  To
      correct this problem, move it later in the list than the overlapping map.

  A - ALTmap:  Displays the map UNDER the current map.  Since APRS always uses
      the latest map in the MAPLIST.xxx file that meets the current cursor
      location and screen range, areas where maps overlap may sometime be
      obscured.  This command displays the next higher map in the list.

  L - Locks the current map.  This defeats the normal APRS auto-map select
      feature so that you will not get a redraw if your cursor gets over
      on another map during a special event.  This also lets you zoom way
      out to see the actual limits of the data in the map file, even if,
      for some reason, the map border is different than the actual data.

  FILES-ChgMapList - This command under the FILES menu, lets you select from
      any number of MAPLIST.xxx files.  In addition to the standard distro
      files of USA, EAS, WES, CEN, and SE, you may also want to customize
      these to your area and give them new names so they are not confused
      with, (or overwritten by), the standard ones.  This also simplifies
      the task of the state APRS map coordinators that can now maintain
      their own MAPLIST.xx files for their states.


METHODS FOR MAKING APRS MAPS

     There are several methods for making maps depending on the resources
available to the user.

  MANUAL     - Ruler and Pencil method.  Most APRS maps (60+) were done this
               way!  Just use a pencil and home-made template to determine
               X,Y offsets from the origin in the upper left corner of the map.
               Then use a DOS editor to enter the X,Y values into a map file.

  MAPFIX     - This program can edit or modify MAP files.  But free-handing of
               the cursor on the screen is difficult to match real world
               coordinates.  This method is best for sketching in local roads
               on existing maps.

  CD ROM     - MAPFIX can also inport data points from the 1:2,000,000 USGS
               CD ROM of the whole USA; but the resolution is only down to the
               state road level, and 3 to 8 hours of manual filtering is
               required to eliminate redundant point data.  See the N.TN map
  100,000    - W7KKE has written a conversion for the USGS 1:100,000 CD ROM,
               but it also takes hours to process the data into a usable and
               meaningful APRS map, since USGS data is VERY fragmented.

  AUTOCAD    - KG8GE has developed programs for building APRS maps to and from
               AUTOCAD.  See the section at the end of this file.

  DIGITIZER  - MAPFIX can accept input from a digitizer tablet.  This makes
               all points very accurate and is the FASTEST way to build a map!

  MOUSE      - MAPFIX can be initialized to use a serial-MICROSOFT-mouse as
               a poor mans mouse.  See MOUSE.txt

  GPS REPLAY - This is the easiest way to add detail in your area.  Just drive
               around with your GPS, saving APRS track history files.  Then use
               MAPFIX to overlay these histories onto the screen for easy cursor
               drawing.

  IMPORTING  - This feature in MAPFIX lets you import into your current
               map, all or a selected category of features from another
               maps.  Re-computing of the Origin and scale is AUTOMATIC. 
               This makes it easy to combine maps.  Take parts from adjacent
               maps to build a map centered on your location.

Look for the sections below that describe each of these methods.  The manual
method is described first, since it gives you the basic structure of the
APRS maps format.

GENERAL CAUTION:  APRS maps are NOT intended, nor expected to fulfill all map
requirements.  APRS maps are intended to provide the user with a visual
reference to where things are in a radio network.  Once you see where a station
is, and you want to see what street he is on, or what address block he is in,
you should refer to printed maps of your area or make a higher detail map.  Do
not waste time trying to put too much detail into APRS maps!  Similarly, don't
try to label everything.  Too many labels makes it hard to see callsigns.
Also, while driving along at 60 MPH and 30 second GPS updates, zooming in
below about 8 miles makes the map move so rapidly so that fine detail is not
needed.  I usually stay at the 16 mile scale to see what is comming ahead.
This confirms that in most cases a straight line between intersections is just
as effective as a very detailed curvy map and only takes 2 points vice 20!  So
concentrate on plotting the intersections accurrately; if you want to come
back later and add more detail curves for artistic sake, that is easy to
do with the MAPFIX.bas program.


HOW TO MAKE APRS MAP FILES:   To see what maps are available to the system,
use the MAPS-BORDERS command.  This command draws the boundaries of all map
files and shows you the areas covered by detail maps.  Some of these maps are
very detail, and some are just "starter" maps to give new users in those
areas a basic map outline from which to add their own detail.  If your local
APRS net does not have at least a 64 mile map, please contact me.   It is
also easy to shift the center and detail of maps to highlight your area.  See
the section MORE ABOUT MAPS at the end of this file for info on how to center,
convert and spawn new maps.  See README\MOREMAPS.txt for a list of some good
map makers and state map coordinators.


OVERALL APRS MAP FILE FORMAT:  In any map file, the first 8 lines define the
origin and scale.  Comment text is permitted on these first 8 lines after the
initial data value and a comma.  See the example map below for Colorado.  The
remainder of the file just lists X,Y points that form the map features
such as roads and rivers.  To end each such feature and begin another, APRS
uses a 0,0 entry.  The next feature begins with the value of the line color,
followed by the feature name.  At the end of this file, is a 0,-1 which marks
the end of points data, and the beginning of the list of map labels.  See the
COLORADO map example below and the section on map labels.


MANUAL DOS TEXT EDITOR METHOD:  Simply use a DOS editor to make a list
of points for APRS to use in drawing line segments.  Note that the coordinates
are listed as X,Y where X is horizontal and Y is vertical.  This is backwards
from the usual order that we list LAT (vert) and LONG (Horizontal), so be sure
to put the horizontal (X) value first. You can use any editor to prepare a map
file.  Simply use a chart that has lat/long references and select an origin
beyond the upper left hand corner of the area you want to cover.  That point is
0,0 and all points are measured from there. (negative numbers are OK if you
later add points behind the origin, but the - is an extra character that slows
down file loading); similarly, an X value of 0 is not permitted since it is used
to indicate separations between the end of one feature and start of another.

MAP SCALE:  Next choose an appropriate scale in pixels-per-degree of longitude
and latitude for the area you want.  Since EGA graphics has a 350/640 pixel
resolution, I have found that 120 pixels per degree (2 pixels per  minute) is
excellent for large state maps.  I used 12 pixels per degree for the whole US.
By keeping the scale number an integer multiple of 60, you avoid any future
roundoff and truncation errors due to ZOOM functions and when converting
points from one map scale to another.  I have used 6,12,24,30,60,120,300,600,
1200, etc.  It takes 1200 pix or more in order to resolve city streets.  If
you use too fine of a scale then you are limited as to how far the map can
extend.  Points with values greater that 999 should be minimized and no values
should be bigger than about 1100 or there is a chance APRS will crash on very
zoomed-in maps.  The further you zoom in, the larger the values become until
you get an overflow error.

MAP RANGE:  Since APRS handles range scales as integer powers of 2, I suggest
making most maps slightly larger than any given power of 2.  This is so that
you can place the cursor near the center of the map, and pretty much see all
of it at once.  To make it easy to hit the center of a map with the cursor, I
make my maps with a range about 10% larger than any power of 2.  To make it
easy to find map centers, APRS shows them with a small +.

MAPLIST.xxx:   This file contains the list of all map files available to APRS
and decides which map is loaded based on the location of the cursor.  The
first 3 lines of the file also contain the default LAT/LONG and Range for
the first map loaded.  The program uses this default to center the first map
each time the program starts up (center of USA).  These values are ignored
when a backup file is loaded using the FILES-LOAD command, or when a registered
user has saved his default location in his CONFIG file.   The MAPLIST.xxx
default location is also stored in the #1 MAP HOT KEY so that you can
instantly zoom out to the default map for that list with a single key stroke.

ADDING MAPS:   To add a map to your system, look at the MAPLIST.xxx file.  It
contains a list of all maps useable by the system.  There can be multiple
MAPLIST.xxx files.  The MAPLIST.USA file comes with the APRS distribution and
contains all regional, and state maps, plus some representative local maps.
You can either add your map to this file, or add it to any local state lists
that might be available.  Currently there are complete MAPLIST.xxx map files
for many states such as Calif, Missouri, and Ohio.  The MAPLIST.OH file lists
over 90 local Ohio maps!

     To add a map, simply add a line that contains the MAPname, LAT, LONG,
MAPrange, and comments.  The LAT/LONG are in decimal degrees and describe
the center of your map.  The MAPrange tells the system to load this map if
the cursor falls within this range of the center.  Actually it is a little
more complicated.  The given map will not be used until the cursor location
plus the current range scale in all directions fully falls within the
boundaries.  HINT - so that your detail map seems to blend in with
the next larger map, add enough rough features and points to your borders to
surround your area with rough detail out to MAX Range beyond.

     Currently APRS can only use 170 maps in MAPLIST.xxx.  To make room for
new maps, but keep old ones handy for later use, You can place a (*) at the
beginning of a line to tell APRS to skip that map.  Also you can add some
comment lines at the designated space in the file (beginning with *) and for
each map so that you can keep track of your maps.  If you have no comments
for a map, you MUST place a comma at the end of the line.

MAP HIERARCHY:  It is important to place maps in decending order.  The last
map in the list that contains the given cursor position will be used.  If a
larger map covering the same area as a smaller map follows it later in the
list, then the larger map will always be found last and will be used, instead
of the desired smaller map.  You can see the this effect, by using the MAPS-
HIERARCHY command.  If maps overlap in your area, use the MAP-ALT command to
temporarily see the map beneath the present map.  You can also use the MAPS-
OVERLAY command to overlay the larger map onto the present map.  Using
this feature, you could make two maps of the same area and scale.  On one you
could put rivers and roads, on the other you could put counties, property
lines, and grids.  Then by listing the gridded map first in the MAPLIST.xxx
file, it would always be superceeded by the road map, but could be summoned
up by hitting the MAPS-OVERLAY command!

MAP FEATURES:  APRS displays all map features by drawing lines from point-to-
point.  Each feature begins with 0,0 followed by the line color and a name for
the feature, followed by pairs of x,y points using the scale you chose.  The
feature name is not used, but is useful for identification during editing.  In
APRS, there is no limit on the number of features, But the total number of
points must remain below 2999.  The MAPFIX.BAS program does, however, have a
finite limit during map editing (currently about 150).  The POINT values
are positive to the right and down.  The end of a feature is simply the 0,0
which starts a new one.  After the last feature, there is a special 0,-1 which
indicates the end of all feature information and the beginning of the labels
list.

MAP COLORS:  APRS recognizes certain map colors for turning on and off
map features.  It typically uses most of the brighter colors.  You can
change the background color with the Tint command or dim all colors using
the MAPS-FEATURES-DIM command.  Map colors are automatically dimmed when
you ask for a MAPS-BORDERS display so that map edges show up brightly.
Here are my standard colors.  The * indicates that the color is uniquely
recognized by the APRS FEATURES command:

 0 - Black (normal background)     * 8 - dark gray (Railroads)
 1 - dim blue                        9 - Bright Blue
 2 - dim green                     *10 - Bright Green (Interstates)
*3 - dim cyan (Rivers)             *11 - Bright Cyan  (Major rivers, Coasts)
 4 - deep red (state roads)        *12 - Bright Red   (major roads)
 5 - dim violet                     13 - Bright Violet(special routes/events)
*6 - dim orange (state/county lines 14 - Bright Yellow (Cities,airports)
*7 - gray     (back roads)          15 - Bright White  (Labels and CALLS)

MAP LABELS:   Labels are drawn on maps at given lat/long coordinates.  The
labels are listed at the end of each map (up to 99).  Each label has a range
scale associated with it, so that more labels can appear at smaller ranges.
The first line in the labels list has a leading 0 and then any any comments.
From then on to the end of the file, each line consists of 4 fields separated
by commas.  First is the label text (up to 12  characters long) followed by
the LAT, LONG and RANGE.  LAT and LONG must be  given in decimal degrees.
The MAPFIX.bas program displays the location of the cursor in decimal degrees
for this purpose.  Labels are plotted right justified.  This means they will
be plotted to the left of the given point.  A way to visualize how a label
will appear is to assume the label has a following period (.) and that the
period is the location where the label will be plotted.  Labels are
right justified so that they do not overprint station callsigns which are all
left justified.   Since absolute LAT/LONG reference is used, labels can be
transferred without any change to any scale map.  You may decide to change
the range size so that the label shows up sooner or later on different maps.

Please note, however, that labels are printed on the normal EGA screen 24 line
raster, so they can be off their exact location by almost a full text line
vertically, and one full character horizontally.  Take this into account
when placing labels.

     You can also build APRS symbols directly into MAPS!  Instead of a text
label, simply make the first three characters of the label be a $ followed
by the symbol character, followed by a hexidecimal number from 1 to F that
indicates the desired color for the symbol.  The remaining 8 characters can be
used for a conventional label at the same location.  For example, look at the
VORTAC's (aircraft nav aids) that I added to the ALASKA maps.  They are listed
in the map file as $VEANC,lat,long,rng.  The V is the VORTAC symbol, the E is
hexidecimal for 14 or the color yellow, and ANC is the label for the ANChorage
VORTAC as it will appear on the map.

            
EXAMPLE:  The following map file constitutes a trivial state map of Colorado.
The first 8 lines are the fixed format lines which define the origin and scale.
Next are the features for the state borders and for Denver.  Finally are
the map labels.  To see how this map looks, move the cursor to the center of
Colorado on the US map and page-down to the 256 mile scale.

  41.0, latitude origin   (equates to 0,0 in)  [Notice how comments can be on]
  110.0, long of origin   (coordinate system)  [the ends of these first lines]
  60, pixels per deg of lat/long               [and 1st line of each new line]
  39,LAT of map center    (For ur reference only. Value in MAPLIST.xxx is what)
  105.5,LON of map center (is actually used as the center and Range for maps  )
  200,MapRange
  0,(reserved)
  * This single comment line can contain anything... more or less
  0,0
  6,Colorado state line
  59,0
  59,240
  479,240
  479,0
  59,0
  0,0
  14,Denver city limits
  300,68
  289,77
  300,85
  311,77
  300,68
  0,-1                            (0,-1 indicates end of map features)
  0,Comments or notes... etc      (   note that the 0, is required   )
  Colorado,40,105,200
  Denver,39,104,100


MAPFIX.BAS:  This QBasic program is a very powerful APRS MAP EDITING tool.
It can be used in several ways to make or fix APRS maps as follows:

   FREEHAND:  Just move the cursor and add points.  Very useful for eyeballing
              in new roads to an existing map.  But can be difficult to get
              roads exactly in place
   CD ROM:    MAPFIX can inport points from the 2,000,000:1 USGS CD ROM, but
              about 5 Mb of points are generated for each 64 mile square area.
              This then takes HOURS to reduce the redundant data to a useful
              APRS MAP
   DIGITIZER: Run MAPFIX with a serial digitizer tablet connected to the COM
              port, and MAPFIX can be used to generate an EXACT map to any
              scale for which you have a paper map.  THIS IS THE BEST WAY TO
              MAKE APRS MAPS! (but requires you to have paper MAPS)
   GPS REPLAY:MAPFIX can overlay an APRS track history file over your map on
              the screen, so that you can easily and accurrately draw maps
   CONVERSION:Using the CONVERSION (F2) command in MAPFIX, you can change the
              origin and SCALE of any existing APRS map so that text from one
              map can be cut and pasted into any other APRS map.  This can be
              used to build large maps out of many small ones, or to customize
              an existing map of your area, using pieces from surrounding areas.
         
   IMPORTING: THis new feature in MAPFIX 6.0 permits you to load into your
              current map, all of a selected category of features from other
              maps.  Re-computing of the Origin and scale is AUTOMATIC!  This
              makes it easy to combine maps.  Take parts from adjacent maps
              to build a map centered on your location.


Using MAPFIX.bas to convert any one map to a different LAT/LONG origin or
different Pixels-per-degree resolution is very useful for customizing maps.
Using the CONVERSION command with the QBasic editor, you can piece together
features from one map to cut and paste into another map.  Say you are building
a fine detail map, but want to use the statelines and interstates from a
larger map.  Just use an editor (or the MAPFIX KILL and TRIM commands) to
remove all unnecessary points from the big map, keeping all the features that
you want to retain and move to your new map.  Then use the F2 (CONVERSION)
command to re-compute the point values to the new origin and scale.  Then use
this new file as the beginning of your new map.  This feature is now improved
with the IMPORT command.  This command will selectively import map features
from other maps into the current map while automatically doing the point
conversions.


MANUAL TECHNIQUE:  Once you have chosen an origin in the upper left hand
corner of your map, all map values will be measured from that point.  Most
maps have LAT/LONG lines around the borders.  If you are using 240 pixels per
degree for a state size map, then each LAT/LONG line corresponds to a multiple
of 240.  Simply mark on the borders of your original map these values 240,
480, 720, etc.  Then make a smaller template which matches the size of one
square of LAT/LONG lines.  Draw a finer grid of lines every 10 pixels on the
template.  Then to locate the coordinates of any point on the map, simply
orient the template with a major LAT/LONG square, and interpolate the point
within the grid on the template which represents a 10x10 pixel area.  Use a
text editor to add these numeric values into the map file.  Every point on
the map can be identified by a pair of X,Y numbers.  Remember that these
offsets are from the origin for THIS map and scale.  For transfering features
from one map scale or origin to another, use the MAPFIX.bas IMPORT command.
Map labels, however use complete LAT/LONG values, so they can be freely moved
among maps.

CAUTION: since many highway maps are Lambert Conformal instead of Mercator
projections, use the center square in your map for making the template to
minimize errors.  Further, be careful of highway maps that only have tick marks
along the borders for LAT/LONG. If the map is not a Mercator projection, then
you cannot just draw a straight line from left to right connecting latitude
marks.  Longitude lines are straight on a Lambert Conformal, but not latitude
lines!

SPECIAL EVENTS:  Conversly, absolute accurracy is only important if there will
ever be a GPS or LORAN station involved in your net.  A map with little
relationship to true LAT/LONG is perfectly useable in some APRS applications
as long as all stations in the net are using the same map and no one is using
GPS.  So feel free to draw quick simple maps for special events even as small
as a few square blocks without worrying about exact LAT/LONG.  Objects on one
station screen will still be in the same location on all other screens!  Use
the Chess board example at 25N 90W to play chess on the air!  But GPS is
comming, be prepared!

                          MORE ABOUT MAPS PART 2


NOTES ABOUT STARTER MAPS:  Some of the larger starter maps that I provided use
a scale of 120 pixels per degree which is suitable for about a 400 mile square
area.  With the whole map visible, one pixel represents about .25 miles.  For
typical states, 360 pixels per degree will give resolution to 0.1 mile and 128
mile range.  One way to begin customizing maps to your area is to take one of
the existing maps and add roads and features in your area.  Since all maps in
the APRS system are limited to a maximum of 2999 data points, however, the
large area maps can usually contain only the major interstates, rivers and
highways.  This is fine for most VHF applications.  But as more and more
people add detail closer to home, smaller maps need to be "spawned" off to
make room for more detail.  The following sections describe how to spawn maps
and convert points from one map to another.


MAP CENTERING:  To change the center and range of a map to match your needs,
simply edit the MAPLIST.xxx file to your desired center and range (rename it
so as not to confuse it with the distro copy).  As the number of points in
your map grows, you may need to throw out some of the points which are beyond
your area of interest.  Use MAPFIX.bas to delete points.  See the next section
on map spawning.

O |                      O |                        O |             O|
----------------------   ------------------------   --------------- ---------
  |          |       |     |         ---------- |     |           |  |
  |  MAP A   |   *   |     |         | MAP C  | |     |           |  |
  |          |       |     | -----------      | |     |        -----------
  |          --------|     | | MAP B | |      | |     |     *  | MAP D   |
  |        *         |     | |       |*|      | |     |        |  |  |   |
  |                  |     | |       --|------- |     |        |  | *|   |
  |                  |     | |         |        |     |--------|--|  |   |
  |                  |     | -----------        |              |---------|
  |                  |     |                    |                    |-------
  --------------------     ----------------------
                                            
   NEW CENTER & RANGE     MAP SPAWNING/CONVERSION       MAP IMPORTING

MAP SPAWNING:  In the figure above, map A is the original map with the origin
at O.  Using 120 pixels-per-degree resolution, all points within a square area
8 degrees on a side (about 400 miles) can be resolved with pairs of 3 digit
numbers.  As the number of points in such a regional area map fills up towards
the 2999 limit, it is necessary to start new smaller area maps such as B, C,
and D above to make more room.  Spawning a new map using MAPFIX.bas is easy.
Simply use the alt-CENTER and alt-RANGE commands to re-draw the white map
border to the location you want, then use the alt-TRIM command to remove all
points outside of that area.   Next use the F2-CONVERSION command to change
the origin closer to the new upper left corner and give a new scale to permit
higher resolution.  Finally, begin adding more finer detail using what ever
technique you intend to use.  Then save the new map and add its name to the
MAPLIST.xxx file.


MAP CONVERSION:  When it is desired to move features and points from one map to
another map which has a different origin (X) or resolution, then use the
CONVERSION (F2) command.  This process can re-compute the values of map points
to a new ORIGIN and/or SCALE.  Once map points have the same ORIGIN and scale,
they can be moved between maps with a text editor.  THIS CONVERSION IS NOW
AUTOMATIC using the alt-IMPORT command.

IMPORTING AND COMBINING MAPS:  The alt-IMPORT command will import all points
of a selected category of features from other maps into the current map. This
can be used to build large maps from small ones, or to build new maps from
pieces of other ones.  See MAP D above.  In this process, all points from the
selected map that fit within the WHITE border of the current map, are imported.
For each pass, you specify the source map, and what category of features to
import.  Select the category by the color number; 6 for boundary lines, 10
for interstates, 11 for coastline, etc.

PIXELS-PER-DEGREE:  Although my early regional maps used 120 pixels per degree,
most of the newer maps generated from my CD rom use at least 450 to 600 pixels-
per degree.  This gives finer detail resolution on the smaller 64 mile maps.
You can use 1200 ppd to resolve down to large city blocks, but to get them
accurately, you should consider 2400 ppd which can resolve down to about 100
feet.  Notice that as you increase the number of pixels-per-degree, you also
reduce the maximum size that a map can cover.  This keeps the numbers from
getting too large and causing an overflow condition.  A 1200 ppd map should
be used for map areas less than 50 miles and so forth.


AUTOCAD MAPS!   Jim Krist KG8GE has done a marvelous job of writing programs
to use AUTOCAD to make APRS maps.  He has done every street in the town of
MARION Ohio.  HIs program is named PLT2MAP and permits you to use a CAD plotter
to make AUTOCAD maps and then convert them to APRS.  Registered copies of his
software can be obtained for $25 from him at 315 Hane Ave, Marion, Ohi0, 43302.

