Towards automating the nautical chart generalization workflow

Figures & data

Figure 1. US/Canadian Border-West Coast (a) current chart scheme (IC-ENC 2022) and (b) planned gridded scheme (NOAA 2023).

Table 1. ENC usage bands and navigational purpose and the respective IHO recommended OCS compilation scales.

ENC Usage Band	Navigational Purpose	Radar	IHO S-57	IHO S-101	Current NOAA	Reschemed NOAA
1	Overview	3,000,000	–	10,000,000	10,000,000	5,120,000
		1,500,000	1,500,000	1,500,000	1,587,870	2,560,000
2	General	1,500,000	1,499,999	1,500,000	1,534,076	1,280,000
		350,000	350,000	350,000	240,000	640,000
3	Coastal	350,000	349,999	350,000	600,000	320,000
		90,000	90,000	90,000	150,000	160,000
4	Approach	90,000	89,999	90,000	150,000	80,000
		22,000	22,000	22,000	25,000	40,000
5	Harbor	22,000	21,999	22,000	51,639	20,000
		4,000	4,000	4,000	5,000	10,000
6	Berthing	4,000	4,000	4,000	12,000	5,000
			–	1,000	2,500	2,500

Table 2. Nautical chart constraints template example.

Nautical Charts specification defined as constraints on (one, two or a group) of objects
Constraint	Feature Class	Geometry	Condition to be respected during Generalization	Pseudo code Example	Theme Hierarchy
Constraints on one Object
Topology	COALNE	Line	Land areas or points that are less than 0.8mm@scale to the Coastline will be merged to the coastline (i.e. the modified coastline should be on the outer boundary of the features).	Extract all LNDARE & COALNE within AOI Calculate Shortest dist. <d> between LNDARE polygons and COALNE lines if <d> between LNDAREs or COALNEs =< 0.8 mm @ scale Merge LNDAREs with COALNE bordering outer LNDARE with no gaps Check for gaps between COALNE & LNDARE and fill it End	5
Safety	DEPCNT	Line	Depth Contours can only move to the deep side	Select all DEPCNT within AOI Identify shallow side & deep side for each DEPCNT as “-” & “+” Start DEPCNT Generalization While generalization DEPCNT line can only move towards “+” regions if any DEPCNT line was displaced towards “-”, flag it as safety violation in a separate geo table End	4
Constraints on two Objects
Topology	DEPCNT/DEPARE	Line/Area	Whenever Depth Areas are modified, the corresponding Depth contours which were Formed from the old depth area limit must be revised to reflect the new location of it with no gaps or overlap	Extract all DEPCNTs & DEPAREs Generalize DEPAREs within SOE Theme Check for topological errors Modify DEPCNTs to coincide with generalized DEPAREs Check For topological errors (gaps or overlaps between DEPCNTs & DEPAREs) Repeat until no errors End	5
Safety	SOUNDG/DRGARE	Point/Area	Dredged area limit must be adjusted to exclude any shoal depths from the area.	Select all DRGAREs within AOI After Generalization & Smooth production of DEPCNTs if a shoal SOUNDG dist. < xmm@scale to a DRGARE Adjust DRGARE to exclude SOUNDG elif a DRGARE width < xmm@scale Collapse DRGARE to line End	4

Figure 2. An abstract schematic description of the automated nautical generalization model (Nada et al. 2022).

Figure 3. The generalization phases and sub-models in ArcGIS Pro.

Table 3. The geometric and generalization relationship (defined in the GRS).

Theme Feature Class & Relation		Description	Valid Geometry
Geometric Relation	SOE	The Types of features that make up the skin of the earth.	Polygon
	Interior	Features that are typically contained within a SOE polygon. When SOE features are generalized, these features should remain within the polygons.	Line
	Edge	Feature that typically share a coincident edge within an SOE polygon (e.g. COALNE), when SOE features are simplified, these features should be generalized the same way to remain coincident with the polygons.	Line
Generalization Relation	Individual	These are line or polygon features that should be generalized individually. Features from the shared and barrier types will be used as barriers during generalization	Line - Polygon
	Shared	Features that contain edges that should be generalized together. Features from the individual and Barrier types will be used as barriers during generalization	Line - Polygon
	Barrier	Features that do not need to be generalized, used as barriers to maintain topological relationships when Individual and Shared features are processed.	Point - Line - Polygon

Figure 4. Removing overlaps between Polygons as per the GRS Hierarchy levels.

Figure 5. Filling gaps between polygons as per the GRS hierarchy levels.

Figure 6. The simplify shared sub-model flow chart.

Figure 7. The generalization model – example on land area and the related features.

Figure 8. The study areas in NY Long Island Sound-USA and completed, in-work, and planned new cells as of March 2023 (NOAA 2023).

Table 4. Current NOAA ENC status as of March 2023 (NOAA 2023).

NOAA ENC Status
Band	5 - Harbor		4 - Approach		3 - Coastal		2 - General		Sum
Number/Percentage	#	%	#	%	#	%	#	%	#	%
All	4391	100%	2377	100%	352	100%	93	100%	7213	100%
Available to Public	608	13.8%	335	14.1%	0	0.0%	2	2.2%	945	13.1%
In Validation	13	0.3%	6	0.3%	0	0.0%	0	0.0%	19	0.3%
In work	58	1.3%	148	6.2%	0	0.0%	0	0.0%	206	2.9%
Planned	3712	84.5%	1888	79.4%	352	100.0%	91	97.8%	6043	83.8%

Table 5. ENC selected S-57/101 features and associated NIS feature classes.

Group	No.	S-57/S-101 Feature class	Feature Class Name	NIS Feature class (FC subtype value)	Point	Line	Area
Group 1	1	LNDARE	Land Area	NaturalFeaturesA (5)	P	L	A
				NaturalFeaturesL (1)
				NaturalFeaturesP (1)
	2	DEPARE	Depth Area	DepthsA (1)	-	L	A
				DepthsL (1)
	3	DRGARE	Dredged Area	DepthsA (5)	-	-	A
	4	FLODOC	Floating Dock	PortsAndServicesA (40)	-	L	A
				PortsAndServicesL (20)
	5	PONTON	Pontoon	PortsAndServicesA (80)	-	L	A
				PortsAndServicesL (35)
	6	UNSARE	Unsurveyed Area	DepthsA (15)	-	-	A
	7	HULKES	Hulk	PortsAndServicesA (60)	P	-	A
				PortsAndServicesP (40)
Group 2	8	COALNE	Coastline (natural)	CoastlineL (1)	-	L	-
	9	SLCONS	Coastline (artificial)	CoastlineL (5)	P	L	A
	10	DEPCNT	Depth Contour	DepthsL (5)	-	L	-
	11	SOUNDG	Sounding	SoundingsP (1)	P	-	-
	12	*ATONS	Aids to Navigation	AidsToNavigationP	P	-	-
	13	*DTONS	Danger to Navigation	DangersP	P	-	-

Figure 9. Research case-1, Block Island North, NY-USA (a) Model input 1:20k (b) Model output 1:40k (c) Model output 1:80k.

Figure 10. Result Case-2, Long Island Sound, NY-USA (a) Before generalization (b) After generalization.

Figure 11. Result Case-3, Block Island South, NY-USA (a) Before generalization (b) After generalization.

Table 6. Topology validation checks (IHO 2018.).

NO	Check description	Check message	Check solution
79	For each feature object of geometric primitive line where a component edge CROSSES another component edge without a connected node at the crossing point.	Component edges of a line object cross without a connected node at the crossing point.	Insert connected node at crossing point.
80a	For each feature object of geometric primitive area where an interior boundary is WITHIN an interior boundary.	Interior boundary within an interior boundary.	Amend boundaries so that the interior boundary is not within another interior boundary.
80b	For each feature object of geometric primitive area where an interior boundary is not WITHIN an exterior boundary.	Interior boundary outside of an exterior boundary.	Amend boundaries so that interior boundary is within exterior boundary.
80c	For each feature object of geometric primitive area where an exterior boundary is WITHIN an interior boundary.	Exterior boundary within an interior boundary.	Amend boundaries so that exterior boundary is not within the interior boundary.
82	For each feature object of geometric primitive line or area which references the same edge more than once.	Object references the same edge more than once.	Remove duplicate reference to the edge.
83	For each node which EQUALS another node (connected or isolated).	Nodes are coincident.	Remove or amend coincident node.

Figure 12. Safety validation tool results (a) Input database (b) Output database with generalization difference (c) Output database with Safety violations (d) Output Database.

Figure A1. The Automated Generalization Model General Flow Chart.

Figure A2. Research Cases (1, 2 and 3) Bar Charts for features before and after generalization.

Figure A3. Topology validation tool results for the three research cases.

Table A1. Case-1 feature counts before and after generalization (only those in bold are used from before generalization for the calculations).

Agent Type	Feature Class group	Group Features	Before Gen.			After Gen.		Gen. Class %	Gen. Group %
			FC #		Group #	FC #	Group #
Macro – Polygons	NaturalFeaturesA	LNDARE_LandArea	96		405	15	15	15.6%	3.7%
		LAKARE_Lake	29			–		–
		LNDRGN_LandRegion	182			–		–
		RIVERS_River	6			–		–
		SEAARE_Sea Area Name Water Area	92			–		–
	DepthsA	DEPARE_Depth Area	977		1,005	114	133	11.7%	13.2%
		DRGARE_Dredged Area	28			19		67.9%
	CoastlineA	SLCONS_Shoreline Construction	12		12	–	0	–	0.0%
Meso – Lines	CoastlineL	COALNE_Coastline	593		1,564	259	529	43.7%	33.8%
		SLCONS_Shoreline Construction	971			270		27.8%
	DepthsL	DEPCNT_Depth Contour	1,012		1,012	118	118	11.7%	11.7%
	NaturalFeaturesL	LNDARE_Land area lines	7		93	–	–	–	–
		RIVERS_River Lines	68			–		–
		SLOTOP_Slope Topline	18			–		–
	PortsAndServiceL	PONTON_Pontoon	46		46	–	–	–	–
Micro – Points	SoundingsP	SOUNDG_Soundings	5,812		5,812	840	840	14.5%	14.5%
	CoastlineP	SLCONS_Shoreline Construction	6		6	0	–	–	–
	DangersP	CTNARE_Caution Area	5		1,202	–	206	–	17.1%
		OBSTRN_Obstruction	67			15		22.4%
		UWTROC_Under Water Awash Rock	1,099			169		15.4%
		WATTUR_Water Turbelnce	1			–		–
		WRECKS_Wreck	30			22		73.3%
	AidsToNavigationP	BCNLAT_Beacon Lateral	38		251	24	132	63.2%	52.6%
		BCNSPP_Beacon Special Purpose	2			2		100.0%
		BOTISD_Buoy Isolated Danger	1			1		100.0%
		BOYLAT_Buoy Lateral	125			97		77.6%
		BOYSAW	2			2		100.0%
		BOYSPP_Buoy Special Purpose	3			2		66.7%
		DAYMARK_Day Mark	40			0		0.0%
		FOGSIG_FogSignal	13			2		15.4%
		LIGHTS_Light	23			1		4.3%
		RDOSTA_Radio Station	1			1		100.0%
		TOPMARK_Top mark	3			0		0.0%
	NaturalFeaturesP	LNDARE_Land area Points	215		225	65	65	30.2%	28.9%
		LNDELV_Land Elevation	6			–		–
		LNDRGN_LandRegion	3			–		–
		SLOGRD_Sloping Ground	1			–		–
	SeabedP	None	0		0	476	476	–	–
Total selected features (underlined)				11,157		2,514		22.5%

Table A2. Case-2 feature counts before and after generalization.

Agent Type	Feature Class group	Group Features	Before Gen.		After Gen.		Gen. Class %	Gen. Group %
			FC #	Group #	FC #	Group #
Macro – Polygons	NaturalFeaturesA	LNDARE_LandArea	130	739	28	28	21.5%	3.8%
		LAKARE_Lake	52		–		–
		LNDRGN_LandRegion	418		–		–
		RIVERS_River	5		–		–
		SEAARE_Sea Area Name Water Area	134		–		–
	DepthsA	DEPARE_Depth Area	765	825	114	168	14.9%	20.4%
		DRGARE_Dredged Area	59		53		89.8%
		UNSARE_Unsurveyed Area	1		1		100.0%
	PortsAndServicesA	GATCON_Gate	1	3	–	0	–	0.0%
		HULKS_Hulk	2		–		–
Meso – Lines	NaturalFeaturesL	LNDARE_Land area lines	2	80	–	0	–	0.0%
		RIVERS_River Lines	57		–		–
		SLOTOP_Slope Topline	21		–		–
	DepthsL	DEPCNT_Depth Contour	823	823	81	81	9.8%	9.8%
	CoastlineL	COALNE_Coastline	1114	2168	353	697	31.7%	32.1%
		SLCONS_Shoreline Construction	1054		344		32.6%
Micro – Points	SoundingsP	SOUNDG_Soundings	5857	5857	685	685	11.7%	11.7%
	DangersP	CTNARE_Caution Area	16	354	–	138	–	39.0%
		OBSTRN_Obstruction	19		18		94.7%
		UWTROC_Under Water Awash Rock	300		112		37.3%
		WATTUR_Water Turbelnce	2		0		0.0%
		WRECKS_Wreck	17		8		47.1%
	AidsToNavigationP	BCNLAT_Beacon Lateral	11	340	11	172	100.0%	50.6%
		BCNSPP_Beacon Special Purpose	31		31		100.0%
		BOYLAT_Buoy Lateral	174		111		63.8%
		BOYSAW	1		1		100.0%
		BOYSPP_Buoy Special Purpose	16		16		100.0%
		DAYMARK_Day Mark	9		0		0.0%
		FOGSIG_FogSignal	2		0		0.0%
		LIGHTS_Light	94		1		1.1%
		RDOSTA_Radio Station	1		1		100.0%
		TOPMARK_Top mark	1		0		0.0%
	NaturalFeaturesP	LNDARE_Land area Points	42	63	65	65	154.8%	103.2%
		LNDELV_Land Elevation	5		–		–
		LNDRGN_LandRegion	16		–		–
	SeabedP	None	0	0	381	381	–	–
Total selected features (underlined)			10,539		2,415		22.9%

Table A3. Case-3 feature counts before and after generalization.

Agent Type	Feature Class group	Group Features	Before Gen.		After Gen.		Gen. Class %	Gen. Group %
			FC #	Group #	FC #	Group #
Macro – Polygons	NaturalFeaturesA	LNDARE_LandArea	6	41	1	1	16.7%	2.4%
		LAKARE_Lake	5		–		–
		LNDRGN_LandRegion	17		–		–
		SEAARE_Sea Area Name Water Area	13		–		–
	DepthsA	DEPARE_Depth Area	180	188	40	48	22.2%	25.5%
		DRGARE_Dredged Area	8		8		100.0%
Meso – Lines	DepthsL	DEPCNT_Depth Contour	211	211	40	40	19.0%	19.0%
	CoastlineL	COALNE_Coastline	39	269	20	80	51.3%	29.7%
		SLCONS_Shoreline Construction	230		60		26.1%
Micro – Points	SoundingsP	SOUNDG_Soundings	1739	1739	540	540	31.1%	31.1%
	DangersP	CTNARE_Caution Area	2	124	–	54	–	43.5%
		OBSTRN_Obstruction	4		1		25.0%
		UWTROC_Under Water Awash Rock	109		46		42.2%
		WATTUR_Water Turbelnce	1		0		0.0%
		WRECKS_Wreck	8		7		87.5%
	AidsToNavigationP	BCNLAT_Beacon Lateral	9	47	6	18	66.7%	38.3%
		BOYLAT_Buoy Lateral	7		6		85.7%
		BOYSAW	1		1		100.0%
		BOYSPP_Buoy Special Purpose	6		4		66.7%
		DAYMARK_Day Mark	9		0		0.0%
		FOGSIG_FogSignal	2		1		50.0%
		LIGHTS_Light	12		0		0.0%
		TOPMARK_Top mark	1		0		0.0%
	NaturalFeaturesP	None	0	0	2	2	–
	SeabedP	None	0	0	67	67	–
Total features in database			2,584		850		32.9%

Table A4. Study area ENC (title, name, edition and scale).

Research Case	No.	Title	Ed.	Update Date	Update	Issue Date	Cell Name	Scale
Case study-1 (Block Island North)	1	North Atlantic Ocean and Block Island Sound from East Point Fishers	1	18-Mar-22	1	31-Mar-22	US5CT1EY	1:20k
	2	Block Island Sound and Mystic River	1	18-Mar-22	0	18-Mar-22	US5CT1FX	1:20k
	3	Block Island Sound – Stonington Harbor to Wequetequock Cove	1	18-Mar-22	0	18-Mar-22	US5CT1FY	1:20k
	4	Block Island Sound	1	17-May-22	0	17-May-22	US5NY2HL	1:20k
	5	Block Island Sound	1	17-May-22	0	17-May-22	US5NY2HM	1:20k
	6	Block Island Sound	1	17-May-22	0	17-May-22	US5NY2HN	1:20k
	7	Block Island Sound	1	18-Mar-22	0	18-Mar-22	US5NY2IL	1:20k
	8	Block Island Sound	1	18-Mar-22	0	18-Mar-22	US5NY2IM	1:20k
	9	North Atlantic Ocean and Block Island Sound – Fishers Island	1	18-Mar-22	1	1-Apr-22	US5NY2JL	1:20k
	10	Approach to Endeavor Shoals and Block Island Sound	1	17-May-22	0	17-May-22	US5RI1BB	1:20k
	11	Block Island Sound	1	18-Mar-22	0	18-Mar-22	US5RI1CA	1:20k
	12	Block Island Sound	1	2-May-22	0	2-May-22	US5RI1CB	1:20k
	13	Block Island Sound – Watch Hill to Atlantic Beach	1	18-Mar-22	0	18-Mar-22	US5RI1DA	1:20k
	14	Block Island Sound	1	2-May-22	0	2-May-22	US5RI1DB	1:20k
	15	Pawcatuck River and Atlantic Beach	1	18-Mar-22	0	18-Mar-22	US5RI1EA	1:20k
	16	Block Island Sound – Entrances to Winnapaug and Quonochontaug Pond	1	3-May-22	0	3-May-22	US5RI1EB	1:20k
Case study-2 (Long Island Sound)	1	North Atlantic Ocean and Shinnecock Bay	2	30-Mar-22	0	30-Mar-22	US5NY2DD	1:20k
	2	North Atlantic Ocean to Shinnecock Inlet to Shinnecock Bay	2	13-Apr-22	1	19-May-22	US5NY2DE	1:20k
	3	North Atlantic Ocean and Heady Creek	2	13-Apr-22	0	13-Apr-22	US5NY2DF	1:20k
	4	North Atlantic Ocean	1	1-Mar-22	0	1-Mar-22	US5NY2DG	1:20k
	5	Flanders Bay to Great Peconic Bay	1	2-Sep-21	0	2-Sep-21	US5NY2ED	1:20k
	6	Great Peconic Bay	2	22-Feb-22	1	11-May-22	US5NY2EE	1:20k
	7	Cow Neck	2	22-Feb-22	0	22-Feb-22	US5NY2EF	1:20k
	8	Long Island, New York – Mecox Bay	2	10-May-22	0	10-May-22	US5NY2EG	1:20k
	9	Mattituck Creek, Brushs Creek, and James Creek	2	31-Jan-22	1	25-Feb-22	US5NY2FD	1:20k
	10	Marratooka Point to Cutchogue Harbor	1	19-Aug-21	1	26-Jan-22	US5NY2FE	1:20k
	11	Little Peconic Bay	1	20-Aug-21	1	26-Jan-22	US5NY2FF	1:20k
	12	Noyak Bay	1	20-Aug-21	1	26-Jan-22	US5NY2FG	1:20k
	13	Long Island Sound	2	13-May-21	0	13-May-21	US5NY2GD	1:20k
	14	Long Island Sound, Goldsmith Inlet	2	13-May-21	0	13-May-21	US5NY2GE	1:20k
	15	Southold Bay	2	12-Jan-22	1	26-Jan-22	US5NY2GF	1:20k
	16	Shelter Island	2	26-Jan-22	0	26-Jan-22	US5NY2GG	1:20k
Case study-3 (Block Island South)	1	North Atlantic Ocean – Long Island, Montauk Beach	1	17-May-22	0	17-May-22	US5NY2FL	1:20k
	2	North Atlantic Ocean	1	17-May-22	0	17-May-22	US5NY2FM	1:20k
	3	North Atlantic Ocean	1	17-May-22	0	17-May-22	US5NY2FN	1:20k
	4	Long Island – Montauk Harbor Entrance	1	19-May-22	0	19-May-22	US5NY2GL	1:20k
	5	Long Island – Lake Montauk and Montauk Point	1	19-May-22	0	19-May-22	US5NY2GM	1:20k
	6	North Atlantic Ocean Approach to Endeavor Shoals	1	17-May-22	0	17-May-22	US5NY2GN	1:20k
	7	Approach to Endeavor Shoals and Block Island Sound	1	17-May-22	0	17-May-22	US5RI1AB	1:20k
	8	Block Island Sound and Approaches	15	2-Feb-22	1	10-May-22	US4CN22M	1:80k

IC-ENC. 2022. “IC-ENC S-57 Catalogue.” Accessed September 30, 2023. https://www.ic-enc.org/our-coverage.

 Google Scholar

NOAA. 2023. “Status of New NOAA ENCs.” Accessed March 20, 2023. https://distribution.charts.noaa.gov/ENC/rescheme/.

 Google Scholar

Nada, T., C. Kastrisios, B. Calder, E. Christie, C. Greene, A. Bethell, and H. Madhu. 2022. “The Nautical Cartographic Constraints and an Automated Generalization Model.” Canadian Hydrographic Conference, Ottawa, Canada, June 6–9.

 Google Scholar

IHO. 2018. ENC Validation Checks (S-58). Ed 6.1.0. Monaco: International Hydrographic Organization.

 Google Scholar

Data availability statement

The data that support the findings of this study are available in figshare at:

https://figshare.com/s/7343dc119ddf6eba00f1.

These data were derived from the following resources available in the public domain: Office of Coast Survey, National Oceanic and Atmospheric Administration https://charts.noaa.gov/InteractiveCatalog/nrnc.shtml#mapTabs-2.