Bathymetry of the Gulf of Maine - December 1999


Name: bathgma (arcs) & bathgmp (polygons)
Format: 2 Shapefiles (1 for arcs & 1 for polys)
METADATA BELOW IS FROM MASSGIS:

OVERVIEW

This datalayer represents seafloor topography for the Gulf of Maine, extending from the Bay of Fundy south of New Brunswick to the Continental Shelf southeast of Nantucket.  The linework in this layer came from an ArcInfo bathymetric contour coverage available through the U.S. Geological Survey's Coastal and Marine Geologic and Environmental Research program, part of its Woods Hole Field Center.  MassGIS assembled the data into a polygon coverage stored in the NE library, named BATHYMGM.

MANUSCRIPT

The USGS collected data from available sources on the Web and from CD-ROM products. The data included digital sounding data, digitized contour line data and previously gridded products from a variety of sources.  Specifically, seven datasets were incorporated to produce a final 15 second grid product:

Bathymetry contour lines were then generated at the following intervals, in meters below sea level,  from the 15 second grid:  -4000, -3000, -2000, -1000, -500, -400, -300, -280, -260, -240, -220, -200, -180, -160,-140, -120, -100, -90, -80, -70, -60, -50, -40, -30, -20, -15, -10, -5

PRODUCTION

MassGIS processed the bathymetry linework coverage to remove dangles and intersection errors and to create polygon topology.  With Arc Macro Language (AML), each polygon was coded for a range of depth below sea level in meters, based on the values of the lines' CONTOUR item.  Additionally, the mainland areas were "sealed off" to create an inland polygon coded with the range "Above -5."  Because there was no zero contour or coastline in the original USGS dataset, this inland polygon represents the shallowest of sea floor topography.  When displaying this layer it is important to draw land features atop the bathymetry; the coastline included in land feature will serve as the zero contour and the area just offshore will appear as the -5 to 0 range.

ATTRIBUTES

The .PAT (polygon attribute table) has the following attributes associated with each polygon:

HIGH

4

5

B

The highest (closest to surface) depth, in meters

LOW

4

5

B

The lowest (farthest from surface) depth, in meters

DEPTHRANGE

14

14

C

The range of values, from the HIGH value to LOW

DEPTHCODE 

2

2

 I

A numeric code based on the DEPTHRANGE value. See following table:

 

DEPTHRANGE

DEPTHCODE

Above -5

1

-5 TO -10

2

-10 TO -15

3

-15 TO -20

4

-20 TO -30

5

-30 TO -40

6

-40 TO -50

7

-50 TO -60

8

-60 TO -70

9

-70 TO -80

10

-80 TO -90

11

-90 TO -100

12

-100 TO -120

13

-120 TO -140

14

-140 TO -160

15

-160 TO -180

16

-180 TO -200

17

-200 TO -220

18

-220 TO -240

19

-240 TO -260

20

-260 TO -280

21

-280 TO -300

22

-300 TO -400

23

-400 TO -500

24

-500 TO -1000

25

-1000 TO -2000

26

-2000 TO -3000

27

-3000 TO -4000

28

Below -4000

29

The .AAT (arc attribute table) has the following attributes:

CONTOUR

4

5

B

Depth below sea level, in meters

This layer also contains three levels of annotation, subclass NAME, for some offshore features.

MAINTENANCE

MassGIS is maintaining this datalayer.  More information on this and related datasets may be found online at http://pubs.usgs.gov/of/1998/of98-801/.  A more generalized and less extensive offshore bathymetry coverage developed by Mass. Coastal Zone Management, BTHOS250, is also available.

 

 


Last updated: March 14, 2011