Overview

Vector products are accessible through the GIBS WMTS and WMS visualization services.  WMTS responses are formatted as gzip-compressed Mapbox vector tiles (specification), or "MVTs", while WMS responses are available as raster images. 

The data behind each visualization service is the same, however the mechanism for styling differs.  A client application is responsible for applying styling to MVTs when using the WMTS API.  Conversely, GIBS applies a default style when rendering vector data as a raster when using the WMS API.  See the Vector Layer Styles section below for more information.

An MVT returned via the WMTS service contains information for a client to draw the features within the user interface, but also a set of properties that contain data associated with the feature.  The Mapbox vector tile specification provides structure for representing these dataThe Mapbox vector tile specification provides structure for including data values as properties associated with a feature, but no mechanism for interpreting the meaning or intended use.  As such, additional metadata is required.  GIBS has developed a specification for defining each property contained within MVTs in its vector products.  See the Vector Layer Metadata section below for more information.

The following sections provide examples for how to detect and interact with vector products within the GIBS WMTS and WMS services

Vector Layer Metadata

As mentioned previously, the Mapbox vector tile specification provides structure for representing these data, but no mechanism for interpreting the meaning or intended use.  As such, GIBS has developed the following specification for defining each property contained within MVTs in its vector products. Each vector product has an associated associated JSON vector layer metadata file which provides the following information:

• A unique identifier for the property, as found in the MVT data itself
• Descriptive information such as a title, description, and the function of the property (e.g. identification vs styling)
• The data type and optional units for the property
• Valid values for the property
• Additional flags for improved UI experience (e.g. "is this optional")

Specification

The following table outlines the content of the GIBS vector metadata specification.  

	Sample Value
Identifier	The unique identifier of the MVT property.	String		FRP
Title	A human readable title for the property.	String		Fire Radiative Power
Description	A human readable description for the property.	String		A measure of the rate of radiant heat output from a fire.
Units	The units value to be applied to the actual value of this property.	String		MW
DataType	The data type of this property.	Enumeration		float
ValueList	A listing of the possible valid values for a 'string' property type, if the property has a controlled list.	Array	Only one may be used	[ "Lake Ice", "Sea Ice", "Not Ice" ]
ValueRanges	A listing of mutually exclusive min and max value pairs representing ranges of valid values for the 'Integer', 'float', and 'datetime' property types.	Array of Objects		[ { "Min": 0, "Max": 99999999 } ]
ValueMap	A map of the possible valid values for 'string' or 'int' property types, and their associated description.  This facilitates a key-value lookup table allowing for a simplified property value (i.e. the ‘key’).	Object		{ 10 : “Processed Fire Pixel”, 20 : “Saturated Fire Pixel” }
Function	The property’s intended function as a part of the visualization product.	Enumeration		Describe
IsOptional	Indicates whether the property is optional.	Boolean		true
IsLabel	Indicates whether the property should be used to label the point in a user interface.	Boolean		true

The following "business logic" rules are applied :

1. One and only non-optional Label
2. Non-duplicate identifiers
3. ValueRange for int, float, datetime
4. Unique ValueList items
5. ValueMap for stirng int
6. Only one non-optional Identify

Examples

A vector layer metadata file is a list of content blocks defining each property. The following snippet shows an example of a single property's definition within the vector layer metadata file.

    {
      "Identifier" : "NumReactor",
      "Title"      : "Number of Reactors",
      "Description": "Number of Active Reactors at a given Plant",
      "Units"      : "Reactors",
      "DataType"   : "int",
      "ValueRanges": [ { "Min": 1, "Max": 9 } ],
      "Function"   : "Style",
      "IsOptional" : false,
      "IsLabel"    : false
    }

The following block provides a full example of a vector layer metadata file.

{
  "id": "Nuclear_Power_Plant_Locations",
  "mvt_properties": [

    {
      "Identifier" : "Plant",
      "Title"      : "Plant Site Name",
      "Description": "Name of Nuclear Plant",
      "DataType"   : "string",
      "Function"   : "Identify",
      "IsOptional" : false,
      "IsLabel"    : true
    },

    {
      "Identifier" : "NumReactor",
      "Title"      : "Number of Reactors",
      "Description": "Number of Active Reactors at a given Plant",
      "Units"      : "Reactors",
      "DataType"   : "int",
      "ValueRanges": [ { "Min": 1, "Max": 9 } ],
      "Function"   : "Style",
      "IsOptional" : false,
      "IsLabel"    : false
    },

    {
      "Identifier" : "p10_30",
      "Title"      : "Population within 30km (2010)",
      "Description": "Total population within a 30km radius of the nuclear plant (2010)",
      "Units"      : "Persons",
      "DataType"   : "int",
      "ValueRanges": [ { "Min": 275, "Max": 7170590 } ],
      "Function"   : "Describe",
      "IsOptional" : false,
      "IsLabel"    : false
    }
}

MVT Metadata Specification

Stuff...

• Identifier [1]
• Title [1]
• Descripition [1]
• Units [0..1]
• Data Type [1]
• Value Ranges [0..1]
• Value List [0..1]
• Value Map [0..1]
• Function [1]
• Is Optional [1]
  
• Is Label [1]

Description

The data type of this property.  Valid values include:

• ‘string’
• ‘int’
• ‘float’
• ‘datetime’ (YYYY-MM-DDTHH:MM:SSZ)

Sample Value

“double”

Description

The property’s intended function as a part of the visualization product.  Possible functions include:

• Identify - Properties that form a “primary key” to identify the visualization product. Often these are used used during processing to separate data points into separate layers (e.g. Platform and Day/Night).  These properties typically would also be in the associated layer metadata (e.g. Platform or Version) and embedded in the layer identifier (e.g. MODIS_Terra_Day_Fires).
• Style - Properties that are utilized for styling or filtering vector features.  These will typically be included in the default style(s) offered through WMS or the Mapbox Style JSONs. 
• Describe - Properties that provide additional information regarding the vector feature (e.g. Acquisition Time or Inclination Angle).  They may be useful for tooltip presentation to users.

Sample Value

“Identify”