Maritime Limits and Boundaries for ArcGIS

Owned by Erlend Kvinnesland
Last updated: Sept 02, 2024
7 min read

Introduction

Maritime Limits and Boundaries for ArcGIS is an addin to ArcGIS PRO that allows you to compute maritime limits and boundaries in ArcGIS PRO.

Main features include:

  • Calculate limit line geoprocessing tool.
  • Calculate equidistant line geoprocessing tool

The extension is under development and more tools will come in the near furture.

Requirements

Maritime Delimitation for ArcGIS requires ArcGIS PRO 3.0 or above. 

License

The add-in uses a cloud based licensing system. Please send an email to support@geocap.no to obtain a user.



Calculate Limit Line 

The Calculate Limit Line tools calculate maritime limits based on a given baseline and distance. The two tools "Calculate Limit Line" and "Calculate Limit Line Multiple Input" will produce the same output. The only difference between the two tools is how the input baseline is organised. Both tools support a combination of "Straight" and "Normal" baselines. The tools use geodesic operations and the resulting limit line will have a high accuracy. 

The tools can produce the following output:

  • The limit line based on user specified distance
  • The polygon of the area between the baseline and the limit line
  • The critical points
  • The connection polygon 


The output feature classes will also create relationships between the different output and the original baseline feature classes. This can be useful in many ways. As an example you can use the Attribute Table dialog to go from a line piece on the distance line to base line feature which was used to produce that line piece.   

The Limit Line

The limit line will consist of many features where each feature is the part of the limit line which share the same base point, or same straight baseline. If the limit line feature is build from a normal baseline, the feature geometry will be an arc. For limit line features build from a straight baseline the geometry is a made using the method of "tracés paralléles" from the straight baseline.

All features will meet the neighboring features in a common point. This common point is accurately calculated using geodesic calculations. This can be where two arcs cross if both base line points are normal baselines. If the baseline has a combination of straight and normal base lines, it can also be a crossing between an arc and a line calculated using the method of "tracés paralléles", or the crossing of two lines using the method of "tracés paralléles". 

The feature table of a limit line will have columns for the original feature class, the original feature object id, the critical points object id, and more. 

The Limit Line Polygon

The limit line polygon will be a combination of the "Calculation Area Polygon" and the generated Limit line. In order for this to be useful, you should spend some time to carefully set up the calculation area polygon. The "inner part" of the calculation area could be a coast line, or the base line. It may have holes if you do not want to include islands. The calculation area could also include boundaries against neighboring states. The algorithm will treat the line pieces of the calculation area polygon as geodesics. If this is not the case, you should use the "Densify" or "Geodetic Densify" tool on the border line piece before you include it in the calculation area polygon.  

The Critical Points

The critical points feature class will consist of the points that have been used to create the limit line. The limit line will have a column with an object id to these points. They will also have a database "relation". The critical point will also have the feature class name, object id, and a relation to the original baseline feature. In addition it has columns with the latitude and longitude of the point.

The Connection polygon

The connection polygon is used to visualize the association between the limit line and the critical baseline points. In the connection polygon feature class, each feature is a combination of the a limit line piece, and the associated base line point or normal base line. The geometry of a connection polygon feature from a normal baseline point will look like a circular sector. The geometry of a connection polygon from a straight baseline will look like a rectangle. 

Using the tools

When using the The "Calculate Limit Line" tool, all baselines should be merged into one feature class. If you use both straight and normal baselines, there should be a column describing if the feature should be treated as a straight or normal baseline. The feature class can have any spatial reference. The result data will have the same spacial reference as the input baseline. The algorithm will use the ellipsoid parameters of the datum of this spatial reference in the geodetic calculations. 


To use the "Calculate Limit Line" tool:

  1. Double-click the tool Calculate Limit Line. The tool dialog will open.
  2. In the field Baseline Feature Class enter the feature class or layer containing the baseline from which the limit line will be calculated.
  3. In the Straight Baseline Attribute enter the name of the column that holds the type of baseline segment attribution. For example, a feature class that holds a mix of straight and non-straight baselins may have a column that for each row marks this part of the baseline belonging to either one of the categories, maybe using labels such as "straight" or "normal".
  4. If the baseline feature class has a baseline type column as described in (3) use this field to enter the attribute value that is used to mark a straight baseline.
  5. In the Distance and Distance Line Unit fields enter the distance to be calculated.
  6. In the field Point Distance Along Distance Line enter the spacing between points along the distance line.
  7. In the field Calculation Area Polygon enter the feature class or layer containing the calculation area. This field is optional.
  8. In the field Output Workspace enter the workspace where the output should be generated. This should be a file geodatabase.
  9. In the field Output Name type in the name which will be used as the first part of the output feature class name.
  10. Tick the output you want the tool to create
  11. Click OK.



When using the "Calculate Limit Line Multiple input" tool, you can use multiple feature classes as input. All features in a feature class will be treated as either straight base lines or normal baselines. If your feature class has a combination of straight an normal baselines, you can "split" the feature class into two layers with different definition queries. The Tool will use the definition query if a feature layer is used as input.

To use the "Calculate Limit Line Multiple Input" tool:

  1. Double-click the tool Calculate Limit Line Multiple Input. The tool dialog will open.
  2. In the field Normal Baselines enter all the feature classes or layers containing the normal baselines
  3. In the field Straight Baselines enter all the feature classes or layers containing the straight baselines
  4. In the Distance and Distance Line Unit fields enter the distance to be calculated.
  5. In the field Point Distance Along Distance Line enter the spacing between points along the distance line.
  6. In the field Calculation Area Polygon enter the feature class or layer containing the calculation area. This field is optional.
  7. In the field Output Workspace enter the workspace where the output should be generated. This should be a file geodatabase.
  8. In the field Output Name type in the name which will be used as the first part of the output feature class name.
  9. Tick the output you want the tool to create
  10. Click OK.




Calculate Equidistant Line


The Calculate Equidistant Line tool calculates an equidistant line between a coastal state and its neighboring countries. The distance can optionally be weighed according to a given attribute field in the baseline feature class. The tools use geodesic operations and the resulting limit line will have a high accuracy. 

The tools can produce the following output:

  • The mid line
  • The mid points 
  • The critical base points
  • The connection lines


The Mid Line

The mid line has a polyline geometry connecting all the mid points. 

The Mid Points

The mid points feature class will have one feature for each point on the mid-line. The Attribute table of a mid points feature class will have columns for the latitude and longitude of the point. The point type, distance to the base points, and information if weights has been applied to any of the base point distances. These are the point types in use: 

  • Equidistant point: is a point with a connection to two base points. If no weights are used, the point has the same distance to both base points. Mid points will be located on the midline line between two turning poinst
  • Turning point: is a point with a connection to three base points. If no weights are used, the point will have the same distance to three base points. The mid line will change direction at these points.
  • Tri point: is the same as a turning point, but the three points will origin from three different feature classes. If the input has a feature class for each country in the calculation, these points will be the tri-points between three countries. 
  • Shared basepoint: is a point on the baseline shared by to neighbouring countries.

The Critical Points

A critical point is a base point which have been used in the midline calculation. This is a point feature class even if the base line input is a polyline or a polygon. 

The Connection lines

A connection line is a line between a Critical point and a point on the mid-line. 


Relations

The output will create relationship between the output feature classes. If the output is stored in the same file geodatabase as the input, the tool will also create a relationship between the critical points feature class, and the input base lines.

A midpoint may be related to two or three connection lines, depending on the point type. Each critical point may be related to many connection lines.



To use the tool:

  1. Double-click the tool Calculate Equidistant Line. The tool dialog will open.
  2. In the field Main Country Baseline Feature Class enter the feature class containing the baseline for the country that has the role of main country in the calculation.
  3. In the Neighouring Country Baseline Feature Classes list add countries that will play the role of neighouring country.
  4. In the Weights field enter the name of the field, if any, that will be used as distance weighing.
  5. In the  Midline Point Spacing, enter the spacing between the points along the mid line. This field is optional. 
  6. In the field Calculation Area Polygon enter the feature class or layer containing the calculation area. This field is optional.
  7. In the field Output Workspace enter the workspace where the output should be generated. This should be a file geodatabase
  8. In the field Output Name type in the name which will be used as the first part of the output feature class name.
  9. Tick the output you want the tool to create  
  10. Click OK.