Delaware Land-Use/Land Cover Transitions
1984 -- 1992

John Mackenzie and Kevin McCullough

Introduction

This study summarizes land-use/land cover (LULC) changes occurring in Delaware between 1984 and 1992.  It is, in part, a follow-up to AES Bulletin 483, Land Use Transitions in Delaware, 1974-1984, published September, 1989, by Mackenzie.  Complete results from this prior study are available in hardcopy.

The present analysis was undertaken by the Spatial Analysis Lab without external funding, and without any contractual commitments to statistical accuracy.  Data inconsistences between the 1984 and 1992 LULC layers, and corrections of some of these inconsistencies, are discussed below.

An analysis of LULC changes between 1992 and 1997 has been completed by the Office of State Planning.  The 1992 and 1997 data were developed from equivalent imagery sources using a consistent classification scheme, and have only minor registration errors.

1984 and 1992 Data

We are distributing the data used in this analysis in both a UTM-18N (NAD83) projection (based on GRS80 spheroid), and unprojected lat-lon decimal degrees.  All data are Arc Export (.E00) format, WinZipped.  The change analysis was performed on the UTM data.  The lat-lon files were processed by Jian Chen, UD Research Data Management Service.

UTM-18N (NAD83) Unprojected (Lat-Lon decimal degrees)
New Castle Co. 1984 LULC (556K) New Castle Co. 1984 LULC (679K)
New Castle Co. 1992 LULC (3.94M) New Castle Co. 1992 LULC (3.44M)
New Castle Co. 1997 LULC (10.8M) New Castle Co 1997 LULC (10.5M)
Kent Co. 1984 LULC (560K) Kent Co. 1984 LULC (646K)
Kent Co. 1992 LULC (5.56M) Kent Co. 1992 LULC (4.79M)
Kent Co. 1997 LULC (14.0M) Kent Co. 1997 LULC (14.0M)
Sussex Co. 1984 LULC (1.00M) Sussex Co. 1984 LULC (1.21M)
Sussex Co. 1992 LULC (8.40M) Sussex Co. 1992 LULC (7.49M)
Sussex Co. 1997 LULC (19.2M) Sussex Co. 1997 LULC (18.6M)

The 1984 LULC series were developed by Earthsat Corp. under contract with the Delaware Dept. of Agriculture at resolution consistent with Landsat MSS satellite imagery (79-meter pixel size), using a modified 2-digit Anderson LULC classification scheme, with a 15-acre minimum mapping unit.  The original data were in Delaware State Plane Projection, NAD 1927, in feet, based on the Clarke 1866 spheroid.

The classification codes for the 1984 LULC series are:

10: undifferentiated urban
11: single family/duplex residential
12: multiple unit residential
13: mobile home residential
14: other residential
15: commercial/service/institutional
16: industrial
17: transportation/communication/utility
18: water-related recreation
19: other recreation
21: agriculture--confined feeding operation
22: other agriculture
30: brushland
41: deciduous forest
42: coniferous forest
43: mixed forest
50: wetland
61: river/canal/estuary/bay/ocean
62: pond/lake/reservoir
71: beach
72: other barren
80: other open/urban

The 1992 and 1997 LULC series was developed by Earth Data (formerly PhotoScience) under contract with the State of Delaware. LULC polygons were digitized on 1-meter resolution digital orthophotos using a different modification of the Anderson LULC classification scheme, with a 4-acre minimum mapping unit. The original data were in Delaware State Plane Projection, NAD 1983, in meters, based on the GRS80 spheroid.

The classification codes for the 1992 and 1997 LULC series are:

110: RESIDENTIAL
    111: single-family dwellings
    112: multi-family dwellings
    114: mobile-home parks
120: COMMERCIAL
    121: retail sales/wholesale/professional services
    122: vehicle-related activities
    123: junk/salvage yards
    125: warehouses
    129: other commercial
130: INDUSTRIAL
140: TRANSPORTATION/COMMUNICATION
    141: highways
    142: parking lots
    143: railroads
    144: airports
    145: communication
    146: marinas/docks
150: UTILITIES
160: MIXED URBAN/BUILT-UP
170: OTHER URBAN
180: INSTITUTIONAL/GOVERNMENT
190: RECREATION
200: AGRICULTURE
    211: cropland
    212: pastures
    213: idle fields
    215: truck crops
    220: orchard/nursery/horticulture
    230: confined feeding operations
    240: farmsteads/farm buildings
    290: other agriculture
300: BRUSHLAND/RANGELAND
    310: herbaceous rangeland
    320: shrub/brush rangeland
    330: mixed rangeland
400: FOREST
    410: deciduous forest
    420: coniferous forest
    430: mixed forest
    440: clear-cut forest
500: WATER
    510: streams/canals
    520: lakes/ponds
    530: reservoirs
    540: bays/coves
600: WETLAND (including forested wetlands)
700: BARREN
    720: beaches
    730: inland sandy areas
    750: extraction areas
    760: transitional/filled/graded areas

There are various inconsistencies between these data sources.

  1. spatial error: The 1992 data, digitized on 1-meter resolution digital orthophotos, have minimal spatial error. The 1984 series, digitized from county maps at 1:100,000 scale, exhibit significant positional error relative to the 1992 data. This analysis made no attempt to correct spatial error in the 1984 data. The spatial error precluded any attempt to develop LULC transition matrices quantifying acres changing between individual LULC categories.
  2. inconsistent resolution: The 1992 series are based on a 4-acre minimum mapping unit, while the 1984 series are based on a 15-acre minimum mapping unit. Therefore prior LULC categories for 1992 polygons smaller than 15 acres are indeterminate. This study treats such small polygons appearing in the 1992 mapping as valid LULC change areas. Although this imparts some upward bias to estimated increases in developed acreage categories, the aggregate acreage in small (4 to 15 acres) residential polygons is relatively minor.
  3. inconsistent classification: The major classification inconsistency involves reassignment of forested wetlands from forest categories in the 1984 mappings to a generic wetland category in the 1992 mappings. There are also discrepancies in the classifications of brushland, individual forest categories, wetland, water, beach and barren land and some individual urban land categories. Some water areas in the 1992 mapping (e.g., the Chesapeake & Delaware Canal) were not included in the 1984 mapping, thus generating some inconsistencies in county acreage totals.

Data Processing

Both series were re-projected to UTM Zone 18 (meters) in ArcInfo, and then imported to GRASS for analysis. All maps were rasterized at 30-meter resolution. Wetland cells in the 1992 maps which were assigned to any forest category in the 1984 maps were re-assigned to that same forest category for 1992. The map series for both years were then reclassified to the following simplified scheme:

 1: residential
 2: commercial/industrial/infrastructure
 3: recreation
 4: agriculture
 5: brushland
 6: deciduous forest
 7: coniferous forest
 8: mixed forest
 9: water
10: wetland
11: barren/beach

Analysis

A graphical frequency analysis of LULC categories in the two series was performed for each county, as well as for the northern and southern halves of New Castle County.  The thumbnail images below access full-screen side-by-side LULC mappings for 1984 and 1992.  Accompanying histograms are included to indicate aggregate acreages in each LULC category in the two mappings, and acreage changes occurring over the 8-year interval between them.  These images are intended to provide a general idea of where the major transitions occurred in each county.

The following tables summarize acreage estimates in each aggregated category.  Some percent change figures reflect significant classification inconsistencies.  Acreage totals do not match mainly because of inconsistent treatment of water features.

These numbers indicate continuing rapid rates of conversion of agricultural and forest lands to residential and other urban uses in all three counties.

  • Sussex County had the largest gross gain and the largest county-wide percent gain in residential acreage (+17,797 acres, +80%). New Castle County below the C&D Canal experienced the most rapid localized rate of residential development (+6,300 acres, +221%).
  • New Castle County had the largest gross gain in other urban uses (+12,649 acres). The portion of New Castle County above the C&D Canal had the largest overall acreage gain (+11,398, +56%) while the area below the C&D Canal had the most rapid rate of gain (+1,251 acres, +210%). Sussex County had the largest county-wide percent gain in other urban uses (+103%).
  • Sussex County had the largest gross loss of agricultural land (-19,746 acres), while New Castle County had the largest percent loss (-16%), with the most dramatic rate of farmland loss occurring north of the C&D Canal (-44%).
  • Sussex County had the largest gross loss of forest acreage (-17,000 acres), while Kent County had the largest county-wide percent loss (-12%). New Castle County below the C&D Canal experienced a 16% net loss of forest acreage.

Change calculations for brushland, individual forest categories, water, wetland and beach/barren categories reflect various classification inconsistencies between the two mappings.

AGGREGATE LAND-USE/LAND COVER CHANGES, 1984 AND 1992
DELAWARE, BY COUNTY
NEW CASTLE COUNTY
NEW CASTLE COUNTY--ABOVE THE C&D CANAL:
                1984 acres  1992 acres   Change    Pct. Chg.
 1 residential     38,999      46,361     7,362       19%
 2 comml/indl      20,468      31,866    11,398       56%
 3 recreation       5,399       5,750       351        7%
 4 agriculture     35,403      19,881   (15,522)     -44%
 5 brushland       11,293       4,767    (6,525)     -58%
 6 decid forest    33,692      31,792    (1,899)      -6%
 7 conif forest       452         492        39        9%
 8 mixed forest       339       1,402     1,063      314%
  [ all forest     34,483      33,686      (797)      -2% ]
 9 water            1,551       3,508     1,957      126%
10 wetland          4,906       2,517    (2,389)     -49%
11 beach/barren     1,125       5,794     4,669      415%
    (TOTALS)      153,626     154,129

NEW CASTLE COUNTY--BELOW THE C&D CANAL:
                1984 acres  1992 acres   Change    Pct. Chg.
 1 residential      2,847       9,146     6,300      221%
 2 comml/indl         596       1,847     1,251      210%
 3 recreation          83          38       (45)     -54%
 4 agriculture     70,409      68,737    (1,671)      -2%
 5 brushland        1,806       1,526      (280)     -16%
 6 decid forest    26,085      21,667    (4,418)     -17%
 7 conif forest       432         291      (141)     -33%
 8 mixed forest     1,167       1,317       150       13%
  [ all forest     27,684      23,274    (4,410)     -16% ]
 9 water              980       4,027     3,047      311%
10 wetland         17,069      12,535    (4,535)     -27%
11 beach/barren       114         931       817      718%
    (TOTALS)      121,587     122,061

NEW CASTLE COUNTY--ALL:
                1984 acres  1992 acres   Change    Pct. Chg.
 1 residential     41,845      55,506    13,661       33%
 2 comml/indl      21,063      33,712    12,649       60%
 3 recreation       5,482       5,788       306        6%
 4 agriculture    105,812      88,617   (17,195)     -16%
 5 brushland       13,098       6,293    (6,805)     -52%
 6 decid forest    59,776      53,458    (6,318)     -11%
 7 conif forest       884         783      (101)     -11%
 8 mixed forest     1,506       2,719     1,213       81%
[ all forest       62,166      56,960    (5,206)      -8% ]
 9 water            2,531       7,534     5,003      198%
10 wetland         21,975      15,052    (6,923)     -32%
11 beach/barren     1,239       6,725     5,486      443%
ALL NEW CASTLE CO 275,211     276,187

KENT COUNTY
                1984 acres  1992 acres   Change    Pct. Chg.
 1 residential     16,857     25,210      8,353       50%
 2 comml/indl       9,119     11,735      2,616       29%
 3 recreation         997      1,234        237       24%
 4 agriculture    195,070    193,380     (1,690)      -1%
 5 brushland        3,914      2,085     (1,829)     -47%
 6 decid forest    99,432     59,061    (40,371)     -41%
 7 conif forest     2,162     14,306     12,144      562%
 8 mixed forest     4,850     20,375     15,525      320%
[ all forest      106,444     93,742    (12,702)     -12% ]
 9 water            5,980      8,493      2,513       42%
10 wetland         44,203     43,377       (826)      -2%
11 beach/barren         0      3,366      3,366       --
ALL KENT CO.      382,584    382,622

SUSSEX COUNTY
                1984 acres  1992 acres   Change    Pct. Chg.
 1 residential     22,295     40,092     17,797       80%
 2 comml/indl       6,862     13,909      7,047      103%
 3 recreation       1,566      1,789        223       14%
 4 agriculture    298,227    278,481    (19,746)      -7%
 5 brushland       26,857     14,578    (12,279)     -46%
 6 decid forest    55,616     24,822    (30,794)     -55%
 7 conif forest    63,865     49,514    (14,351)     -22%
 8 mixed forest    92,593    120,739     28,146       30%
[ all forest      212,074    195,075    (16,999)      -8% ]
 9 water           22,853     30,248      7,395       32%
10 wetland         29,898     42,855     12,957       43%
11 beach/barren     2,445      7,050      4,605      188%
ALL SUSSEX COUNTY 623,078    624,078

DELAWARE
                1984 acres  1992 acres   Change    Pct. Chg.
 1 residential     80,996    120,808     39,812       49%
 2 comml/indl      37,044     59,356     22,312       60%
 3 recreation       8,045      8,811        766       10%
 4 agriculture    599,109    560,479    (38,630)      -6%
 5 brushland       43,870     22,957    (20,913)     -48%
 6 decid forest   214,824    137,342    (77,482)     -36%
 7 conif forest    66,911     64,603     (2,308)      -3%
 8 mixed forest    98,949    143,833     44,884       45%
[ all forest      380,684    345,778    (34,906)      -9% ]
 9 water           31,363     46,275     14,912       48%
10 wetland         96,077    101,284      5,207        5%
11 beach/barren     3,684     17,141     13,457      365%
ALL DELAWARE    1,280,872  1,282,887