J . P.
Dangermond
Director
E n v i r o n m e n t a l Systems R e s e a r c h
380 N e w Y o r k Street
Redlands, CA
92373
H.W. Grinnell, Jr.
U r b a n / R e g i o n a l Economist
Southern C a l i f o r n i a Edison
2244 Walnut G r o v e A v e n u e
R o s e m e a d , CA
91770
Institute
Company
D E V E L O P M E N T OF A N UPDATING SYSTEM A N D
PROCEDURES FOR THE LAND USE PLANNING
I N F O R M A T I O N A N D FORECASTING SYSTEM
A T SOUTHERN C A L I F O R N I A EDISON COMPANY
ABSTRACT.
T h i s paper d e s c r i b e s a two year effort
to develop effective and economic m e a n s for updating
SCE's land use data files using p h o t o i n t e r p r e t a t i o n
of h i g h altitude imagery and b a s e y e a r land use p o l y gon m a p s .
The current SCE land u s e program, the need
for updating it and the impact of updating are first
described; then the alternative updating m e t h o d s
w h i c h w e r e tested, the findings and the recommended
p r o c e d u r e s are d i s c u s s e d .
Special attention is g i v e n
to the p r o b l e m of " s l i v e r " polygons created by o v e r laying updated p o l y g o n s on old m a p s .
Finally, graphical and s t a t i s t i c a l d a t a products effective in showing the m a g n i t u d e and composition of land use change
are described and some are illustrated.
SCE'S CURRENT LAND USE INFORMATION PROGRAM
1
Since 1972 Southern C a l i f o r n i a Edison Company (SCE) has
b e e n developing and applying automated geographic information
systems
to its land use forecasting p r o g r a m .
The present SCE
system w a s initially developed for manipulating and displaying
land use d a t a w h i c h had b e e n derived from remotely sensed imagery.
M o r e recently the interest in the system has expanded to
include e n v i r o n m e n t a l information from a variety of sources.
T h e land use forecasting effort supports four g e n e r a l company
f u n c t i o n s : 1 ) the development of general facility p l a n s for'sub-
1.
The software used throughout this project was the P o l y g o n Information Overlay System (PIOS) developed by E n v i r o n m e n t al Systems Research Institute in the 1970's.
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t r a n s m i s s i o n systems (these plans are used to facilitate c o m m u n ications b e t w e e n the Company and county planning agencies);
2 ) the development of environmental impact reports in relation
to siting facilities w h e r e urban land use is a factor; 3) capital budget p l a n n i n g for distribution system facilities and
4 ) the siting of distribution substations.
Since its inception the p r o g r a m h a s b e e n characterized by
joint planning and cost sharing by the C o m p a n y and counties for
the development of the land use data b a s e s .
T h i s arrangement
h a s resulted in reducing costs for b o t h p a r t i e s and creating
m a c h i n e r e a d a b l e data files that otherwise might not have b e e n
developed.
A n added benefit of this c o o p e r a t i o n h a s been that
the C o m p a n y and the major counties in its service a r e a are w o r k ing from i d e n t i c a l land use data b a s e s in d e v e l o p i n g their r e spective p l a n s .
Geographic
coverage
By the end of 1978 coverage for the land use inventory at
SCE included a l l urbanized areas w i t h i n its service area, e x cept those in Santa Barbara and V e n t u r a C o u n t i e s .
(For these
c o u n t i e s land use n e a r the coast h a s b e e n p h o t o i n t e r p r e t e d and
m a p p e d a s part of a parallel C o a s t a l E n v i r o n m e n t a l and Land U s e
Inventory P r o g r a m . )
Furthermore, it h a s b e e n S C E ? s policy to
develop land use inventories for urban areas not served by the
C o m p a n y but contiguous to its service area.
Most significant of
these a r e a s is southern Orange C o u n t y — an important growth area
at p r e s e n t — and the cities of Burbank, G l e n d a l e , Los A n g e l e s ,
P a s a d e n a and R i v e r s i d e .
In all, the counties that w i l l have
b e e n covered by the end of 1979 are: Inyo, Kern, L o s A n g e l e s ,
O r a n g e , R i v e r s i d e , San Bernardino and T u l a r e Counties.
P r e v i o u s o v e r v i e w of the p r o g r a m ' s
methodology
R e a d e r s are referred to the authors* earlier paper in the
P r o c e e d i n g s ot the A t l a n t a M e e t i n g in 1976 (1) for a more d e tailed d e s c r i p t i o n of the b a s i c m e t h o d o l o g y being used to create
land use i n f o r m a t i o n .
Only an overview of this m e t h o d o l o g y w i l l
be given here.
Land use interpretation and m a p p i n g
T h e first step in creating the information is i n t e r p r e t a tion of land use from aerial p h o t o g r a p h y .
T h i s m a p p i n g is done
at a scale of 1 : 2 4 , 0 0 0 using 50 to 60 c l a s s i f i c a t i o n s chosen to
b e consistent w i t h county planning n e e d s .
M a p p i n g r e s o l u t i o n is
n o m i n a l l y 2.5 a c r e s , but strip development is actually m a p p e d at
a finer r e s o l u t i o n .
Automated
procedures
F o u r automated p r o c e d u r e s are used in d e v e l o p i n g - t h e
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land
use inventory data b a s e : 1 ) digitizing of m a n u s c r i p t maps and
i n i t i a l file creation, 2 ) editing and final file creation,
3) overlay p r o c e s s i n g and 4 ) graphic output p r o c e s s i n g .
D i g i t i z i n g and file
creation
T h e p h o t o i n t e r p r e t e d p o l y g o n manuscript map is digitized by
m o u n t i n g it on a table and recording e a c h polygon representing
h o m o g e n e o u s land use as a series of X,Y coordinate points.
This
p r o c e s s results in an unedited m a c h i n e r e a d a b l e polygon file.
T h e d i g i t i z e d information is initially stored in a micro comp u t e r and then transferred to a m i n i c o m p u t e r for subsequent
editing and p r o c e s s i n g .
Editing and final file
creation
T h e r e a r e s e v e r a l phases of file e d i t i n g .
In ^ . . p r e l i m i n ary edit p o l y g o n files for each v a r i a b l e (such as land u s e ) are
entered as d i s k files; an on-line edit is then done for basic
a c c u r a c y of record formation, i n t e r n a l consistency of coding,
m i s s i n g or d u p l i c a t e p o l y g o n s , polygon closure, etc;
In the graphic edit a plotted p o l y g o n map or C R T graphic
display is produced and visually compared w i t h the m a n u s c r i p t
m a p to check that the locations of p o l y g o n s , lines and p o i n t s
are w i t h i n acceptable tolerances.
E r r o r s in map codes, land use
codes and map identification are detected for on-line edit.
M o r e complex editing problems are solved using editing s o f t w a r e .
F i n a l l y , p o l y g o n v e r t i c e s are adjusted to eliminate g r a p h i c a l
p r o b l e m s that have o c c u r r e d .
A final file is created for each v a r i a b l e for e a c h 7 - 1 / 2
minute base map.
In this P I O S file e a c h p o l y g o n is defined by
two records; the first contains d e s c r i p t i v e information and the
second contains the string of X,Y coordinates that define the
polygon.
Overlay
analysis
In the typical SCE land use study, overlay analysis is
used to calculate and aggregate land use by geographic areal
units such as census tracts and SCE service districts.
The
overlay p r o g r a m d e t e r m i n e s the common areas of two p o l y g o n sets:
the " m a j o r " set (e.g., census tract or service d i s t r i c t ) and the
" m i n o r " set (e.g., land use polygons).
The program employs a
line i n t e r s e c t i o n routine w h i c h d e t e r m i n e s the locations of
i n t e r s e c t i o n s b e t w e e n the two sets of p o l y g o n s .
The program
then r e s t r u c t u r e s the two p o l y g o n files into one file of polyg o n s w h i c h h a v e common a t t r i b u t e s (e.g., of land use and census
tract).
The c l a s s i f i c a t i o n s and areas of the p o l y g o n s are then
summarized according to the m a j o r p o l y g o n .
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G r a p h i c and s t a t i s t i c a l
output
T h e overlay p r o g r a m e n a b l e s P I O S to produce b o t h p o l y g o n
listings and s u m m a r y r e p o r t s of land use by census tract, SCE
service district and c o m m u n i t y - o r i e n t e d units of a n a l y s i s w h i c h
are g r o u p s of census tracts, called s u b r e g i o n s .
T h e other form
of user-oriented output produced by the P I O S software is h i g h
quality land use m a p s drawn on stable b a s e m y l a r .
These maps
m a y b e drawn to any scale, but for SCE land use studies they are
d r a w n and registered to the 7 - 1 / 2 m i n u t e U S G S quad sheets.
U s e of land use d a t a in the forecasting
process
The inventory of current land use is one of the basic data
items used to g e n e r a t e f o r e c a s t s of p o p u l a t i o n , h o u s i n g , e m p l o y m e n t and land use.
Current land use is first related to socioe c o n o m i c v a r i a b l e s on a . s m a l l area, c o m m u n i t y - o r i e n t e d b a s i s ;
these areas are called s u b r e g i o n s .
U s i n g these data, h i s t o r i c a l
information, trends developed from past censuses, and in-depth
interviews w i t h p l a n n i n g o f f i c i a l s and p u b l i c and private sector
sources k n o w l e d g e a b l e in the e c o n o m i c s of the regions and the
c o m m u n i t i e s , the s u b r e g i o n a l and county f o r e c a s t s of p o p u l a t i o n ,
h o u s i n g and land use are m a d e for 5, 10 and 20 y e a r s .
F o r e c a s t . c h a n g e s in land use are m a p p e d in a generalized
w a y so that they can b e overlaid or related to land use polygon
m a p s that are produced in color by P I O S .
These forecasts, together w i t h supporting analyses and
d i s c u s s i o n s , are presently b e i n g p u b l i s h e d in the form of Land
U s e Study R e p o r t s and distributed to u s e r s inside the C o m p a n y ,
cities in the study area, county planning d e p a r t m e n t s and selected o r g a n i z a t i o n s outside the C o m p a n y .
T h e r e p o r t s are p u b l i c
d o c u m e n t s , a v a i l a b l e to a n y o n e .
T H E N E E D FOR U P D A T I N G A N D P O S S I B L E
I M P A C T S ON T H E I N F O R M A T I O N SYSTEM
T h e p r o b l e m of updating the data in automated g e o g r a p h i c
information systems occurs in a n u m b e r of c o n t e x t s .
First,
m a n y files of g e o g r a p h i c information are created not for c o n tinued use but for just a single project; such d e c i s i o n s may be
d u e to the p r o b l e m s f o r s e e n in updating the files later on.
Second, in m a n y k i n d s of automated geographic information
s y s t e m s (including p a r c e l files) updating is a t t e m p t e d ; but w h e n
e v e n limited u n r e l i a b i l i t y is detected and cannot b e isolated
and rectified, the e n t i r e data base often b e c o m e s suspect and
m a y — gradually or r a p i d l y — fall into disuse.
T h i r d , in systems like SCE's, w h e r e continuing updating is required, it is
s o m e t i m e s p o s s i b l e to rely on governmental agencies for updated
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data; sometimes, h o w e v e r , this is not p o s s i b l e .
SCE's service
a r e a b o u n d a r i e s cross many s e p a r a t e g o v e r n m e n t a l j u r i s d i c t i o n s
and the Company cannot rely entirely on g o v e r n m e n t a l units to
p r o v i d e updated information in a consistent form.
T h u s SCE has
turned to the p h o t o i n t e r p r e t a t i o n of remote sensing to p r o v i d e
timely, r e l i a b l e and economic updating of its information.
For most of SCE's forecasts to have continued utility and
c r e d i b i l i t y updating must be carried out fairly frequently.
As
s o o n as key v a r i a b l e s are departing significantly from forecast
values an
u p d a t e is n e e d e d .
S h o r t - r a n g e forecasts (in this
case, 5 to 10 y e a r f o r e c a s t s ) are particularly sensitive to this
need for u p d a t i n g .
U p d a t i n g is required to reflect changes i n b o t h the p a t t e r n s of development and in the total a r e a s devoted
to e a c h land use.
T h e criticality of t h i s p r o b l e m usually
d e p e n d s u p o n the extent to w h i c h a p a r t i c u l a r area is e x p e r i e n c ing g r o w t h .
Land use u p d a t e
needs
In SCE's experience there appear to b e essentially two
types of land use u p d a t e n e e d s : 1 ) the need to update the c u r rent status of the land use inventory information and 2 ) the
need to update the related forecasts of population, h o u s i n g ,
e m p l o y m e n t and land use, p a r t i c u l a r l y by small a r e a s .
T h e updated land use i n f o r m a t i o n also provides trend d a t a
that w e r e not available for the o r i g i n a l studies.
These are
d a t a on land use transactions that have occurred b e t w e e n the
o r i g i n a l study and the update (or, in future, b e t w e e n the
updates).
T h i s land use transaction trend data is of p a r t i c u l a r
interest, b o t h to understanding e l e c t r i c a l load growth in the
Company and to supporting growth m o n i t o r i n g studies at the city
and county l e v e l .
Updating
frequency and coverage
requirements
H o w often does land use updating need to be done and what
is the a p p r o p r i a t e coverage for a land use data base update and
a forecast update?
These two q u e s t i o n s are clearly interrelated,
The m e a n s for detecting h i g h growth areas are readily a v a i l a b l e
(e.g., b u i l d i n g permit data, m e t e r set d a t a ) .
If one is g o i n g
to b e selective and d i f f e r e n t i a t e b e t w e e n areas experiencing
h i g h and low growth then one can, in effect, update h i g h g r o w t h
a r e a s at one frequency and low growth areas at another.
If
threshold growth or s t r u c t u r a l change c r i t e r i a can be d e v e l o p e d
then, in p r i n c i p l e , areas can be updated at v a r i a b l e f r e q u e n c i e s
depending upon the amount and d e g r e e of change and the i m p o r t ance of that change.
At SCE, based on interviews w i t h distribution facility
p l a n n e r s , it a p p e a r s that the need is for updates of land use
status and change in h i g h growth areas every two to three y e a r s
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and for low growth areas there does not appear to be a need to
update at all.
F a c i l i t y siting, on the other hand, a p p e a r s to
require updating of b o t h land use status and f o r e c a s t s about
every five y e a r s for all areas experiencing any growth at all.
These c o m b i n e d r e q u i r e m e n t s appear to be c o m p a t i b l e w i t h the
n e e d s of city and county growth m o n i t o r i n g s y s t e m s as w e l l .
A L T E R N A T I V E S F O R U P D A T I N G L A N D USE DATA FILES
2
In most e x i s t i n g automated information systems p r o v i s i o n
for updating files already exists; what we w e r e looking for in
this study w a s the most effective and a p p r o p r i a t e w a y of u p d a t ing land use.
The study had, in fact, three o b j e c t i v e s :
1.
T o define p r o c e d u r e s w h i c h would e f f e c t i v e l y produce an
u p - t o - d a t e d a t a file so that information could be used in
the same w a y it w a s in the o r i g i n a l land use s t u d i e s .
2.
T o d e t e r m i n e m e t h o d s for creation of ah updated d a t a
file w h i c h could be compared efficiently w i t h the old file
to understand the land use change as distributed s p a t i a l l y .
3.
T o develop p r o c e d u r e s in computer p r o g r a m s w h i c h w o u l d
allow for interfacing the old and n e w files to p r o d u c e
a p p r o p r i a t e m a p s and tabular outputs.
T h i s is a m i d - p r o j e c t report on d e v e l o p i n g c o s t - e f f e c t i v e
t e c h n i q u e s to meet these o b j e c t i v e s .
In p u r s u i n g them three
a l t e r n a t i v e m e t h o d s of updating w e r e e x a m i n e d .
T h e three
m e t h o d s require q u i t e different processing techniques;
these
d i f f e r e n c e s in p r o c e s s i n g time and technology represent the most
significant d i f f e r e n c e s b e t w e e n the three a l t e r n a t i v e m e t h o d s .
Reinterpreting
a complete m a p —
c r e a t i n g new
files
P r o c e s s i n g of an entirely new land use map is subject to
the same c o n s t r a i n t s , p r o b l e m s and time factors w h i c h occurred
in the creation of the original land use files.
The advantage
of this method is the relative ease of producing an internally
consistent new data file rather than replacing p o r t i o n s of an
existing file.
2.
ESRI, w o r k i n g w i t h N A S A , is examining and testing the use of
Landsat remote sensing imagery to flag pixels w h e r e land use
change a p p e a r s to h a v e occurred.
These pixels are then related
to the p o l y g o n s of an existing geographic information system and
a list of the p o l y g o n s w h i c h may have changed is printed out.
The list is then used to guide p h o t o i n t e r p r e t e r s in identifying
areas needing attention during the updating effort.
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T h e m a j o r d i s a d v a n t a g e of this method is that the e x i s t i n g
d a t a file is completely d u p l i c a t e d .
The existing valid d a t a is
d u p l i c a t e d w h i l e the invalid d a t a is b e i n g updated.
Since the
n e w d a t a file has b e e n produced from an entirely n e w effort,
overlay a n a l y s i s may produce spurious p o l y g o n s in areas w h e r e
the two files are m i s - r e g i s t e r e d ; this is the "sliver" or
" s p l i n t e r " polygon p r o b l e m .
Reinterpret
changed a r e a s —
deleting and adding
polygons
U s i n g this m e t h o d , n e w m a n u s c r i p t m a p s w h i c h indicate the
p o l y g o n s to be deleted and those to be added are p r e p a r e d .
A
s e p a r a t e list is prepared for p o l y g o n s w h i c h maintain their
o r i g i n a l b o u n d a r i e s but change in c l a s s i f i c a t i o n .
D e l e t i o n of
e x i s t i n g polygon d a t a and changing codes of existing p o l y g o n s is
a r e l a t i v e l y simple p r o c e d u r e w h i c h can be a c c o m p l i s h e d u s i n g
the o r i g i n a l data file.
P r o b l e m s are encountered w h e n adding n e w p o l y g o n s in the
deleted a r e a s .
The b o u n d a r i e s m a y not exactly match the a d j a c ent p o l y g o n b o u n d a r i e s due to different imagery or inaccurate
drafting.
T h i s can result in m i s - r e g i s t r a t i o n and "sliver" p o l y g o n s b e t w e e n the o r i g i n a l p o l y g o n s and adjacent new b o u n d a r i e s .
T h e solution to this problem is to locate b o u n d a r i e s as
a c c u r a t e l y a s possible and follow this w i t h the n o r m a l p r o c e d u r e
for p r o d u c i n g a " c l e a n " file.
T h i s p r o c e d u r e involves m a t c h i n g
p o i n t s along adjacent b o u n d a r i e s and editing to insure that the
b o u n d a r y lines are c o n t i g u o u s .
The new data file can then be
o v e r l a i d on the old file to produce c a l c u l a t i o n s of area of land
use c h a n g e s .
Reinterpret
changed a r e a s —
update file by overlay
analysis
U s i n g this m e t h o d , only n e w land use boundaries are drafted
on n e w m a n u s c r i p t m a p s and d i g i t i z e d .
T h e resulting files of
changed line segments are overlaid on the existing d a t a files
and a c o m p u t e r p r o g r a m m a k e s the required boundary c o n n e c t i o n s
and code changes in the data file.
The method p e r m i t s rapid
u p d a t i n g and comparison of land use data by automated analysis
rather than by h u m a n - i n t e n s i v e m e t h o d s .
T h e m a j o r problems associated w i t h this method are related
to m i s - r e g i s t r a t i o n of lines and m i s - r e g i s t r a t i o n of points
(vertices) used to identify lines.
If the update data file u s e s
exactly the same v e r t i c e s to d e s c r i b e an existing line the o v e r lay p r o g r a m is able, to update the p o l y g o n by adding n e w lines to
s u b d i v i d e the existing p o l y g o n into two or more n e w p o l y g o n s .
T h i s r e q u i r e s that the same v e r t i c e s w h i c h w e r e used to create
the o r i g i n a l data file be digitized for the update file w h e r e
the n e w lines meet w i t h the existing lines.
If this is not d o n e
the overlay program does not recognize the identify of the o r i g inal and the updated forms of the same b o u n d a r y line.
This
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n o n - i d e n t i t y can result in the creation of e r r o n e o u s p o l y g o n s
which produces erroneous calculations.
Correct r e g i s t r a t i o n of
e x i s t i n g lines and v e r t i c e s requires an intensive map p r e p a r a tion effort using the o r i g i n a l m a n u s c r i p t m a p s to locate v e r t ices.
T h e advantage of speed from automated updating m a y be
offset by the increased p e r s o n n e l and computer time required to
i n s u r e identical line and v e r t e x locations and correct p o l y g o n
closures.
F i n d i n g s on r e c o m m e n d e d
procedures
T h e most a c c u r a t e and straightforward m e t h o d for p r o d u c i n g
a current land use file is to do a complete n e w study.
The data
and b o u n d a r i e s are then consistent w i t h i n the study area.
However, if this n e w file is overlaid on the old file, errors m a y
occur d u e to m i s - r e g i s t r a t i o n of the two studies unless the
o r i g i n a l b o u n d a r i e s are used in the p r e p a r a t i o n of the u p d a t e .
T h e least p e r s o n - t i m e for map preparation and d i g i t i z i n g
o c c u r s w h e n only those areas w h i c h have b e e n changed are i d e n t ified and r e m a p p e d .
E a c h existing map p o l y g o n must be examined
for change by a p h o t o i n t e r p r e t e r (but see footnote 2), h o w e v e r ,
since only changed p o l y g o n s a r e redigitized there are s i g n i f i cant savings in d i g i t i z i n g time.
Old p o l y g o n s are deleted and
n e w ones substituted in their place for d i g i t i z i n g .
Overlay
a n a l y s i s is straightforward since the n e w b o u n d a r i e s are based
o n the o r i g i n a l p o l y g o n b o u n d a r i e s in those areas c o n t i g u o u s to
land use change.
U s i n g this approach a saving of b e t w e e n 20 and
40 percent over the cost of completely redoing a land use survey
can be r e a l i z e d .
M a j o r technical p r o b l e m s occur w h e n n e w p o l y g o n d a t a is
overlaid a u t o m a t i c a l l y to replace existing polygons since
" s l i v e r " p o l y g o n s can result.
A c c u r a t e replacement of an old
p o l y g o n b o u n d a r y w i t h a n e w line requires that the n e w line be
composed of the same v e r t i c e s originally used. A u t o m a t e d p o l y g o n closure a l s o requires continued research and d e v e l o p m e n t .
T h e p r o b l e m of sliver
polygons
T h e m a j o r b a r r i e r to automated updating by overlay is the
inability to a d e q u a t e l y h a n d l e "sliver" p o l y g o n s .
These
" s l i v e r " or " s p l i n t e r " polygons occur in updating chiefly w h e n
o v e r l a y i n g old and n e w p o l y g o n m a p s .
If an old and a n e w p o l y gon are overlaid in w h i c h the b o r d e r s are almost the same line,
or are intended to be the same line, but in w h i c h the a c t u a l
b o r d e r s ' locations d i f f e r . s l i g h t l y , "sliver" or "splinter"
p o l y g o n s or "fuzzy e d g e s " are created.
A l t h o u g h simply stated,
this p r o b l e m is extremely complicated to deal w i t h .
There appear to be four g e n e r a l m e t h o d s for h a n d l i n g
fuzzy e d g e s and splinter p o l y g o n s :
- 243 -
these
1.
D e l e t e p o l y g o n s of m i n i m u m size,
For s t a t i s t i c a l tabu l a t i o n s , s m a l l r e s i d u a l p o l y g o n s falling b e t w e e n overlaid p o l y g o n s are deleted according to some set m i n i m u m area size. T h i s
e f f e c t i v e l y r e d u c e s the total map area of p o l y g o n coverage by
the sum a r e a of the m i n i m u m polygons w h i c h have b e e n deleted
so s t a t i s t i c a l tabulations are inaccurate unless adjusted to
c o m p e n s a t e for the deletions.
For a p p l i c a t i o n s involving g r a p h ic output the a p p r o a c h is often unacceptable since the ragged
polygon edges remain.
2.
Selection of a single line from dominant or s u b o r d i n a t e
overlaid p o l y g o n s .
In this solution a single line is selected
to represent the two or m o r e lines w h i c h h a v e n e a r l y c o m m o n p o s itions.
A u s e r specified algorithm s e l e c t s one of the two c o m m o n lines, d e l e t i n g the o t h e r ( s ) e n t i r e l y .
T h e p r o b l e m h e r e is
that e i t h e r the dominant or subordinate p o l y g o n set is m i s r e p resented and the resulting statistics can b e m i s i n t e r p r e t e d .
3.
R a n d o m s e l e c t i o n of line segments to be used in c o n structing r e s i d u a l p o l y g o n .
T h i s is similar to the second m e t h o d , a b o v e , except that the selection of the line is done on a
random b a s i s , s o m e t i m e s selecting the dominant and s o m e t i m e s
the s u b o r d i n a t e one.
A v a r i a t i o n of this involves selection
among the a l t e r n a t i v e s based simply o n w h i c h p r e s e n t s the g r e a t est a d v a n t a g e s at i n t e r s e c t i o n s .
4.
Line averaging.
This approach involves a rather e l a b o r a t e set of logic w h e r e i n any two or m o r e lines w h i c h generally
follow the same p a t h are compared relative to each other in
terms of their d i r e c t i o n as w e l l as their adjacency and an a v e r a g e line is calculated to represent the two.
T h e r e are two approaches for doing this:
coordinate averaging and v e c t o r a r r a n g i n g .
The first approach is s i m p l e and
direct but e x t r e m e l y limited as a solution.
It involves the
a v e r a g i n g of adjacent or nearly adjacent coordinate p o s i t i o n s
that occur in s i m u l t a n e o u s o v e r l a y s .
To operate effectively the
two lines m u s t run p a r a l l e l to one another and be separated by
only a small d i s t a n c e .
If ending points are not adjacent and
lines cross or are not p a r a l l e l the p r o b l e m b e c o m e s m o r e d i f f i cult.
T h i s sort of situation r e q u i r e s some sort of total v e c t o r
averaging and c o o r d i n a t e c r e a t i o n .
T h e second a p p r o a c h , v e c t o r arranging, r e q u i r e s the ability
to a l i g n similar or adjacent v e c t o r s w h i c h m o v e in, or close to,
parallel positions.
In doing this, overlay and splinter r e m o v a l
can take s e v e r a l a p p r o a c h e s : selecting an average direction
b e t w e e n vectors; compositing pieces of v e c t o r s ; m o v i n g in v a r y ing d i r e c t i o n s ; assuming that one overlay has m o r e dominance in
its l o c a t i o n a l p o s i t i o n that another overlay; etc.
The algorithm r e q u i r e d checks e a c h line according to a subset of i n f o r m a t i o n (e.g., length, direction, adjacency, e t c . ) and selects
an a v e r a g e v e c t o r w h i c h subsequently connects to the end p o i n t s
- 244 -
of the two other v e c t o r ' s polygons w h e r e they change in d i r e c tion.
At present we b e l i e v e that no suitable system for v e c t o r
a r r a n g i n g exists.
T h i s is an area in w h i c h ESRI is c o n t i n u i n g
to do some research.
LAND U S E UPDATE DATA PRODUCTS
DEVELOPED
O n e of the most important products of the update p r o c e s s
the g e n e r a t i o n of s t a t i s t i c a l p r i n t o u t s related to land u s e
change.
T h e s e highlight and summarize change by area and by
s p e c i f i c p o l y g o n s w i t h i n the area.
is
In d e v e l o p i n g the p r o p e r format for these p r i n t o u t s , S C E
and E S R I had several m e e t i n g s on design criteria and s p e c i f i c
layout.
T h e r e s u l t s are three basic printouts, described
below.
P o l y g o n listings representing land
use t r a n s f o r m a t i o n s and status
T h i s output lists all polygons, e s p e c i a l l y noting those
w h i c h h a v e changed.
T h e list is by.map m o d u l e , census t r a c t ,
special' district or some other unit and represents not only
e x i s t i n g land use but also the former land use for p o l y g o n s that
h a v e changed.
T h e format is illustrated in Figure 1.
FIGURE 1
C O M P L E T E LISTING NOTING
POLYGONS FOR MAP MODULE
CHANGES
10
PAGE
7
POLYGON
CENTROID,
POLYGON A R E A
POLYGON NORTH-EAST
POLYGON
SQUARE
SQUARE
FORMER
CODE
(THOUSANDS) N U M B E R
ACRES MILES
KILOMETERS
CODE
RT
AO
RT
PX
RT
RS
232232231231231231-
241
241
241
240
241
243
263.02
263.03
263.04
264.00
265.00
266.00
7.5
5.0
9.9
4.5
12.7
10.0
0.01
0.01
0.02
0.01
0.02
0.02
0.03
0.02
0.04
0.02
0.05
0.04
AO
AO
N o t e e s p e c i a l l y h o w the decimals are used to d e s i g n a t e
p o l y g o n s subdivided through land use change. In this listing
the p r o g r a m first tabulates polygon w h i c h have changed in g e o m etry or c l a s s i f i c a t i o n , then those w h i c h h a v e changed only in
g e o m e t r y , and finally the unchanged p o l y g o n s .
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Land u s e s u m m a r i e s showing net
change
T h i s lists a c r e a g e s for each use for the current year arid
for the b a s e y e a r and changes in land use.
Summarized land use
c a t e g o r i e s are a l s o tabulated.
The format is illustrated in
F i g u r e 2.
FIGURE 2
G R A P H I C S U M M A R Y OF C H A N G E
S O U T H E R N C A L I F O R N I A EDISON U P D A T E STUDY
C H A N G E S IN L A N D U S E F R O M 1974 T O i977
R E D L A N D S Q U A D - M O D U L E 10
LU CODE/
I-
AREA
D E S C R I P T I O N ^DATEl A C R E S
RS
S F A M RES
1974
1977
CHANGE
RM
1974
M FAM RES
1977
CHANGE
7592.5
7751.7
-159.1
582.4
721.5
-139.1
1—PERCENT
SQ M I SQ KM I V A L . 0
11.86
12.11
-0.25
0.91
1.13
-0.22
OF STUDY
AREA—
20
30:731 17.6 IXXXXXXXXXX
31; 371 17.9 IX30CXXXXXXX
-0.641
0.4 I
2.361
1.3 IX
2:921
1.7 IX
- 0 . 5 6 1 0.3 I
A n o t h e r p r e s e n t a t i o n of these data is in the foinn of a
s u m m a r y of land u s e transactions.
It is produced for each
census tract, map m o d u l e ; e t c .
It shows a s u m m a r y of all land
use changes; the former polygon code and the n e w polygon c o d e s
are shown.
T w o i n d i c a t o r s are a l s o p r e s e n t e d : the average
acres per y e a r of change and the annual absorption rate p e r c e n t age.
F i g u r e 3 i l l u s t r a t e s this format.
FIGURE 3
S U M M A R Y OF L A N D U S E T R A N S A C T I O N S
S U M M A R Y OF L A N D U S E T R A N S A C T I O N S 10/74 to 10/77
PAGE 1
SOUTHERN C A L I F O R N I A EDISON U P D A T E STUDY
ACRES
FORMER
PRESENT
AREA
SQ. PER
ANNUAL ABSORPTION
LAND USE LAND USE
ACRES
SQ.MI. KILO.
YEAR RATE PERCENTAGE
A
AC
A
RS
U1
345.449
5.463
87.686
SUBTOTAL
438.599
AO
11.883
0.540
0.009
0.137
1.398 8 6 . 3 6 2
0.022
1.366
0.355 21.922
78.76
1.25
19.99
100.00
0.019
0.048
- 246 -
2.971
0.69
P o l y g o n m a p s of land use transformations and
status
T h r e e types of these niaps w e r e g e n e r a t e d .
F i r s t , a simple
land u s e plot showing the updated alpha code.
Second, a plot of
p o l y g o n s w i t h selected a g r i c u l t u r a l arid undeveloped p o l y g o n s
showing alpha codes and p o l y g o n sequence n u m b e r s .
(Where u p dated p o l y g o n s are created by splitting previous polygons the
h e w p o l y g o n s h a v e an a d d i t i o n a l two digit n u m b e r reflecting a
s u b - s e q u e n c e n u m b e r i n g of the subdivided p o l y g o n . )
Third, a
land use plot of p o l y g o n s w h i c h shows polygon sequence n u m b e r s ;
U p d a t e d p o l y g o n s h a v e codes plotted in a different c o l o r .
C o m p u t e r g r a p h i c s s u m m a r i z i n g land use
change
We h a v e e x p e r i m e n t e d w i t h several v a r i e t i e s of shaded and
colored graphicsi representing cfensus tracts according to s u m m a r y land use c h a n g e information, etc.
A common problem with
these m a p s is that the d a t a are an e x p r e s s i o n of absolute
v a l u e s w i t h i n a v a r i a b l e sized polygon;
T h i s can be m i s l e a d i n g
to the v i e w e r ; larger p o l y g o n s can dominate a display even though
the c h a n g e w h i c h occurred w i t h i n them may be the same or p e r h a p s
smaller than those p o l y g o n s w h i c h are smaller in size.
T h i s is
a c l a s s i c c a r t o g r a p h i c problem to w h i c h v a r i o u s a n s w e r s e x i s t .
CURRENT ACTIVITIES AND PLANS
T h i s y e a r a land use pilot update study is b e i n g carried
out in San B e r n a r d i n o C o u n t y .
T h e study area is about 250
square m i l e s in the East Valley area w h i c h includes the cities
of R e d l a n d s and San B e r n a r d i n o .
The p u r p o s e s of this study are:
1 ) to g a i n the e x p e r i e n c e of carrying out an update study for a
significant g e o g r a p h i c a l area; 2 ) to m o v e the update m e t h o d o l o g y
forward to include updating of p o p u l a t i o n , h o u s i n g , employment
and land use forecasts; 3) to c o m p l e t e development of c o m p u t e r
g r a p h i c s t e c h n i q u e s for c o m m u n i c a t i n g land use change i n f o r m a tion to study users; and 4 ) to test the fit b e t w e e n land use
study u p d a t e s and the n e e d s of county growth m o n i t o r i n g
programs.
REFERENCES
(1)
D a n g e r m o n d , J.P., and G r i n n e l l , H.W., J r . .
"Land U s e Studies at Southern C a l i f o r n i a E d i s o n :
The Development and U s e
of a Land U s e Oriented P l a n n i n g Information System", U R I S A
Annual Conference Proceedings.
S e p t e m b e r 1976.
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