1. What purpose should symbology serve in GeoPackage?
OGC Geopackage SWG
GeoPackage Symbology
What purpose should symbology serve in GeoPackage?

2. Symbology Need Statement
A symbolic mechanism is needed in geopackage to exchange minimum necessary information, thus allowing the receiving system to render the feature using a symbolic representation of the feature.

3. Use Case #1: Military Symbology (MIL-STD-2525, NATO APP6)
GeoPackage Vectors with MIL-STD-2525 metadata
Symbology Set Designation
Symbol ID
Text Modifier(s)
Graphic Modifier(s)
Control Point Geometry
1 Point
2 Points
3+ Points
Each Revision and Change Notice of MIL-STD-2525 and NATO APP6 requires a distinct designation, as the symbol ID encoding and modifier set are not uniform across standards version or even change notices within the same revision.
MILSTD-2525D and APP6(C) have added a second symbol ID, which further complicates backwards compatibility.

4. MILSYM A point feature using symbology will encode only the:
Symbology set designation (eg. MILSTD-2525B-CN1, MILSTD-2525A-CN2, NATOAPP6B)
Symbol ID (encoding appropriate for designated symbology set)
Text and modifier information (encoding appropriate for symbology set)
Control point geometry (if it differs from rendered geometry)
Tactical control point symbology greater than one point often deviates geometry and rendering locations.

5. Use Case #2: Technical Symbology (No Modifiers)
GeoPackage Single Point Vectors with Technical Symbology Identifiers
Symbology Set Designation
Symbol ID
Single Control Point Geometry

6. TECHNICAL SYMBOLOGY Representative Symbology Sets
Australian All-Hazards Symbology –
Canadian Emergency Management Symbology –
European INDIGO Symbology –
Homeland Security Emergency Response Symbols (HSWG-ERS) -
Portuguese Disaster Response Map Symbols (DRMS) -
United Nations OCHA Humanitarian Aid Symbology-
World Meteorological Organization Oceanographic Symbols -

7. Use Case #3: Feature Styling
GeoPackage Vectors with Style ID
Vector attributes specify a Style ID
Style ID refers to a Style “table” that contains
Line Style (Color, Width, Transparency, Dash, Miter, End, …) information (i.e. Symbology Encoding Standard)
Fill Style (Pattern, Transparency)
Styles may be shared or feature unique
Style rules are identified by numeric or alphanumeric identifier
Roughly equivalent to older generation “FACC + GeoSym” Capability

8. Use Case #4: Semantic Styling
GeoPackage Vectors with Semantic Style Description
Vector attributes specify Style Definition
Style contains
Line Style (Color, Width, Transparency, Dash, Miter, End, …) information (i.e. Symbology Encoding Standard)
Fill Style (Pattern, Transparency)
Styles may be shared or feature unique
Style rules are identified by semantic type identifiers

9. Use Case #5: Geometry Styling
GeoPackage Single Point Vectors with Feature Codes to identify feature styling rules.
Rules should accommodate multiscale rendering (Level of Detail).
Rules should allow delineation of geometry type (See TENET Report, Section 3.3)
TENET Report on Symbology Encoding Standard

10. Use Case #6: User-Defined Symbology
GeoPackage Single Point Vectors with embedded or “internal” style reference.
Rules should allow delineation of geometry type (See TENET Report, Section 3.3)
TENET Report on Symbology Encoding Standard

11. Out of Scope Encoding detailed symbology rendering instructions.
Complex spatial geometries (out of scope)
Geometry Style (out of scope)
Constructive (out of scope)
Subtractive geometry (out of scope)

12. UC2 Technical Symbology
Capability Matrix UC
Capability
UC1 MILSYM
UC2 Technical Symbology
UC3 Feature Symbology
UC4 Geometry Style
UC5 Semantic Style
UC6 User Defined
Single Point 
Multiple Control Points ?
Text Modifiers
Graphic Modifiers
Multiscale Rendering

13. Requirements DESCRIPTION RQMT
GPKG symbology information SHALL be limited to the minimum symbol library set, symbol identifier, geometry and representation modifier information required to convey the semantic content of the symbol presentation.
1.0
GPKG features SHALL encode only per-instance symbology information that is minimally sufficient and required to permit an external rendering engine with appropriate symbology set reference library to render a symbol at designated coordinate(s), to include single point symbology, as well as multiple control point symbology.
2.0
GPKG SHOULD NOT encode feature symbology rendering instructions that can be expressed as rendering rules or rendering instructions within an external, “well-known” symbol library.
3.0
GPKG MAY encode primitive geometry styling directives that can be expressed as rendering rules or rendering instructions . E.g. line and fill styles
4.0
GPKG MAY encode user-defined symbology as self-contained renderable sprites, (e.g. PNG, SVG )
5.0
GPKG SHALL encode instance-specific information, such as text or graphic modifiers, (e.g. MIL-STD-2525, NATO APP6 modifiers)
GPKG symbology information SHALL be limited to the minimum symbol library set, symbol identifier, geometry and representation modifier information required to convey the semantic content of the symbol presentation.
GPKG features SHALL encode only per-instance symbology information that is minimally sufficient and required to permit an external rendering engine with appropriate symbology set reference library to render a symbol at designated coordinate(s), to include single point symbology, as well as multiple control point symbology.
GPKG SHOULD NOT encode feature symbology rendering instructions that can be expressed as rendering rules or rendering instructions within an external, “well-known” symbol library.
GPKG MAY encode primitive geometry styling directives that can be expressed as rendering rules or rendering instructions . E.g. line and fill styles
GPKG MAY encode user-defined symbology as self-contained renderable sprites, (e.g. PNG, SVG )
GPKG SHALL encode instance-specific information, such as text or graphic modifiers, (e.g. MIL-STD-2525, NATO APP6 modifiers)