Magnetic Isolines (Foundation)

The path to and name of the feature class, elevation raster, or elevation raster dataset for which you want to generate isolines. This field is required.

A query expression Magnetic Isolines can use to determine which data to analyze when you run the tool. Use this field if you want to generate magnetic isolines for data that meets certain criteria. Type SQL query syntax to specify this criteria.

The elevation data required by the tool. If your input data is non-raster, the tool will apply the altitude value you type in this field globally to the input (or selection set). If your input data is an elevation raster, the altitude data you provide will have no significance.

The value you provide must be between 0 and 1000000. Note that the value does not get applied to the input or output data; the tool just uses it for its calculations.

You must choose the type of linear units you want to use for altitude. Choices include points, feet, yards, miles, nautical miles, millimeters, centimeters, meters, kilometers, decimal degrees, and decimeters.

The linear units of measurement you want to use for the altitude. Choices include points, feet, yards, miles, nautical miles, millimeters, centimeters, meters, kilometers, decimal degrees, and decimeters.

The date for which you want magnetic field values to be calculated. The date must be between the years 2005 and 2010 (the last date available in this release is 12/31/2009). Type the date in mm/dd/yyyy format.

The path to and name of a line feature class or line layer to which the tool will output data. If you type the path to and name of an existing feature class or layer, the tool will overwrite it. If you type the path to and name of a new feature class or layer, the tool will create a new one to store the output data.

Make sure the path includes a geodatabase (most feature classes must be stored in a geodatabase).

The magnetic field variable for which you want isolines generated. You must choose one. Descriptions of each variable are below.

• Declination (isogonic)-The angle between magnetic north and true north. Each isoline created by the tool will connect points with the same declination angle value.
• Inclination (isoclinic)-The angle between a compass needle and the plane of the horizon; it changes as you change latitude. This is also known as magnetic dip or the dip of the compass needle. Each isoline created by the tool will connect points with the same inclination value.
• Annual drift (isoporic)-The change in a year in magnetic field intensity due to changes in currents in the Earth's core. Each isoline created by the tool will connect points with the same annual drift value.
• North field component-The northerly intensity of the geomagnetic field, also known as X. Each isoline created by the tool will connect points with the same north field component.
• East field component-The easterly intensity of the geomagnetic field, also known as Y. Each isoline created by the tool will connect points with the same east component.
• Vertical field component-The vertical intensity of the geomagnetic field, also known as Z. Each isoline created by the tool will connect points with the same vertical component.
• Horizontal intensity-A strength value determined using north and east components (but you do not have to provide north and east component values in order to have the horizontal strength computed). This is also known as H. Each isoline created by the tool will connect points with the same horizontal intensity.
• Total intensity (isodynamic)-A strength value computed using horizontal and vertical components. You do not have to provide values for horizontal and vertical intensity components in order to have the tool calculate total intensity. Each isoline created by the tool will connect points with the same total intensity value.
• Grid variation (isogriv)-The angle between magnetic north and grid north. To use this value for isoline generation, you must be using a coordinate system of Lambert Conformal Conic type. This is a continental projected coordinate system. If your input feature class is not Lambert Conformal Conic and if your data frame is not projected to it, you may have to specify Lambert Conformal Conic in the environment settings.

For details about the logic Magnetic Isolines uses to determine spatial reference, see "How the spatial reference is determined for grid variation" in the tool's geoprocessing overview topics (click the Help icon above, then in the left panel of the dialog box that appears, click Magnetic > Magnetic Isolines, click Related Topics, then click "How the spatial reference is determined for grid variation".

The size you want each cell in the raster to be. The raster in this case is either the raster you provided as input data or the temporary raster the tool generates to calculate isolines for non-raster input data. The temporary raster is also known as the constant raster.

The size you type into this text box determines how many cells the raster will be divided into by the tool. The number of cells in a raster determines its resolution.

To calculate this number of cells, the tool uses the cell size you give it here and either the width or height — whichever is shortest — of the extent of the input data. For example, if the size of your raster is 1,000 units by 1,500 units and you type 2 in this text box, the tool will divide the raster into 500 cells.

If you do not provide a cell size value, the tool uses a value that divides the raster into 250 cells. This default cell size value displays in this text box as soon as you specify an input, but you can change it before you run the tool to any cell size you want.

If a coordinate system is defined for/associated with the raster, the size units are linear units; otherwise they are raster pixels.

A magnetic value the tool uses in the isoline interval method. The isoline interval method is one of two methods you can use to generate isolines.

With this method, isolines are drawn based on two values you provide, a base value and an interval value. The base value is the magnetic value for which you want the tool to start generating isolines. The interval value is the increment for which you want the tool to generate lines after it generates the base value line. Technically, the lines aren't actually generated until you open the output in ArcMap or ArcCatalog; but the information to draw the lines is created and stored in the output. The output is always a new line feature class.

The units for both values are the same as those specified for the magnetic field variable you chose to calculate. Inclination and declination are in decimal degrees. The other variables' units are nano Teslas.

For example, if you chose declination as the magnetic value you want to calculate and provided a base value of 0 and an interval value of 3, the tool:

(1) Takes the input feature class/data you gave and altitude values and computes declination values in decimal degrees for all of the input data.


(2) Creates a set of intermediate rasters in a temporary directory; they are deleted after the tool has finished its computations.


(3) Creates a shapefile named wmmpoint in your C:\Documents and Settings\<user name>\Local Settings\Temp directory and creates a raster named WMMInRaster in the same directory. These items also appear in the ArcMap table of contents if you have ArcMap open.


(4) Creates the information needed to draw isolines (to draw a line between each set of points that have the same magnetic value) on the map. Stores only the line information needed to draw the lines at the base and interval magnetic values you specified.


When you open the output in ArcMap or ArcCatalog, a line will be drawn that connects all points that have 0 decimal degrees as their declination value; a line will be drawn that connects all points that have 3 decimal degrees as their declination value, then one for all points that have 6, then 9, and so on.

An increment value the tool uses in the isoline interval method. The isoline interval method is one of two methods you can use to generate isolines. Type a numeric value in this field (and one in the base value field) if you want to use this method.

With this method, isolines are drawn based on two values you provide, a base value and an interval value. The base value is the magnetic value for which you want the tool to start generating isolines. The interval value is the increment for which you want the tool to generate lines after it generates the base value line. Technically, the lines aren't actually generated until you open the output in ArcMap or ArcCatalog; but the information to draw the lines is created and stored in the output.

The units for both values are the same as those specified for the magnetic field variable you chose to calculate. Inclination and declination are in decimal degrees. The other variables' units are nano Teslas.

For example, if you chose declination as the magnetic value you want to calculate and provided a base value of 0 and an interval value of 3, the tool:

(1) Takes the input feature class/data you gave and altitude values and computes declination values in decimal degrees for all of the input data.


(2) Creates a set of intermediate rasters in a temporary directory; they are deleted after the tool has finished its computations.


(3) Creates a shapefile named wmmpoint in your C:\Documents and Settings\<user name>\Local Settings\Temp directory and creates a raster named WMMInRaster in the same directory. These items also appear in the ArcMap table of contents if you have ArcMap open.


(4) Creates the information needed to draw isolines (to draw a line between each set of points that have the same magnetic value) on the map. Stores only the line information needed to draw the lines at the base and interval magnetic values you specified.


When you open the output in ArcMap or ArcCatalog, a line will be drawn that connects all points that have 0 decimal degrees as their declination value; a line will be drawn that connects all points that have 3 decimal degrees as their declination value, then one for all points that have 6, then 9, and so on.

A list of magnetic values that the tool uses in the Isoline Value List method to compute how isolines should be drawn. In this method, the tool takes the first magnetic value you provide (the first value in the list) and draws a line connecting all of the points that have the first magnetic value. It takes the second value you provide and draws a line connecting all of the points that have the second magnetic value, and so on until it has drawn a line for every value you provided.

Which magnetic value (variable) the tool uses in its computations is determined by which variable you have selected in the tool's Magnetic Field Parameter drop-down list.

The path to and name of the feature class, elevation raster, or elevation raster dataset for which you want to generate isolines. This field is required.

A query expression Magnetic Isolines can use to determine which data to analyze when you run the tool. Use this field if you want to generate magnetic isolines for data that meets certain criteria. Type SQL query syntax to specify this criteria.

The elevation data required by the tool. If your input data is non-raster, the tool will apply the altitude value you type in this field globally to the input (or selection set). If your input data is an elevation raster, the altitude data you provide will have no significance.

The value you provide must be between 0 and 1000000. Note that the value does not get applied to the input or output data; the tool just uses it for its calculations.

You must choose the type of linear units you want to use for altitude. Choices include points, feet, yards, miles, nautical miles, millimeters, centimeters, meters, kilometers, decimal degrees, and decimeters.

The linear units of measurement you want to use for the altitude. Choices include points, feet, yards, miles, nautical miles, millimeters, centimeters, meters, kilometers, decimal degrees, and decimeters.

The date for which you want magnetic field values to be calculated. The date must be between the years 2005 and 2010 (the last date available in this release is 12/31/2009). Type the date in mm/dd/yyyy format.

The path to and name of a line feature class or line layer to which the tool will output data. If you type the path to and name of an existing feature class or layer, the tool will overwrite it. If you type the path to and name of a new feature class or layer, the tool will create a new one to store the output data.

Make sure the path includes a geodatabase (most feature classes must be stored in a geodatabase).

The magnetic field variable for which you want isolines generated. You must choose one. Descriptions of each variable are below.

• Declination (isogonic)-The angle between magnetic north and true north. Each isoline created by the tool will connect points with the same declination angle value.
• Inclination (isoclinic)-The angle between a compass needle and the plane of the horizon; it changes as you change latitude. This is also known as magnetic dip or the dip of the compass needle. Each isoline created by the tool will connect points with the same inclination value.
• Annual drift (isoporic)-The change in a year in magnetic field intensity due to changes in currents in the Earth's core. Each isoline created by the tool will connect points with the same annual drift value.
• North field component-The northerly intensity of the geomagnetic field, also known as X. Each isoline created by the tool will connect points with the same north field component.
• East field component-The easterly intensity of the geomagnetic field, also known as Y. Each isoline created by the tool will connect points with the same east component.
• Vertical field component-The vertical intensity of the geomagnetic field, also known as Z. Each isoline created by the tool will connect points with the same vertical component.
• Horizontal intensity-A strength value determined using north and east components (but you do not have to provide north and east component values in order to have the horizontal strength computed). This is also known as H. Each isoline created by the tool will connect points with the same horizontal intensity.
• Total intensity (isodynamic)-A strength value computed using horizontal and vertical components. You do not have to provide values for horizontal and vertical intensity components in order to have the tool calculate total intensity. Each isoline created by the tool will connect points with the same total intensity value.
• Grid variation (isogriv)-The angle between magnetic north and grid north. To use this value for isoline generation, you must be using a coordinate system of Lambert Conformal Conic type. This is a continental projected coordinate system. If your input feature class is not Lambert Conformal Conic and if your data frame is not projected to it, you may have to specify Lambert Conformal Conic in the environment settings.

For details about the logic Magnetic Isolines uses to determine spatial reference, see "How the spatial reference is determined for grid variation" in the tool's geoprocessing overview topics (click the Help icon above, then in the left panel of the dialog box that appears, click Magnetic > Magnetic Isolines, click Related Topics, then click "How the spatial reference is determined for grid variation".

The size you want each cell in the raster to be. The raster in this case is either the raster you provided as input data or the temporary raster the tool generates to calculate isolines for non-raster input data. The temporary raster is also known as the constant raster.

The size you type into this text box determines how many cells the raster will be divided into by the tool. The number of cells in a raster determines its resolution.

To calculate this number of cells, the tool uses the cell size you give it here and either the width or height — whichever is shortest — of the extent of the input data. For example, if the size of your raster is 1,000 units by 1,500 units and you type 2 in this text box, the tool will divide the raster into 500 cells.

If you do not provide a cell size value, the tool uses a value that divides the raster into 250 cells. This default cell size value displays in this text box as soon as you specify an input, but you can change it before you run the tool to any cell size you want.

If a coordinate system is defined for/associated with the raster, the size units are linear units; otherwise they are raster pixels.

A magnetic value the tool uses in the isoline interval method. The isoline interval method is one of two methods you can use to generate isolines.

With this method, isolines are drawn based on two values you provide, a base value and an interval value. The base value is the magnetic value for which you want the tool to start generating isolines. The interval value is the increment for which you want the tool to generate lines after it generates the base value line. Technically, the lines aren't actually generated until you open the output in ArcMap or ArcCatalog; but the information to draw the lines is created and stored in the output. The output is always a new line feature class.

The units for both values are the same as those specified for the magnetic field variable you chose to calculate. Inclination and declination are in decimal degrees. The other variables' units are nano Teslas.

For example, if you chose declination as the magnetic value you want to calculate and provided a base value of 0 and an interval value of 3, the tool:

(1) Takes the input feature class/data you gave and altitude values and computes declination values in decimal degrees for all of the input data.


(2) Creates a set of intermediate rasters in a temporary directory; they are deleted after the tool has finished its computations.


(3) Creates a shapefile named wmmpoint in your C:\Documents and Settings\<user name>\Local Settings\Temp directory and creates a raster named WMMInRaster in the same directory. These items also appear in the ArcMap table of contents if you have ArcMap open.


(4) Creates the information needed to draw isolines (to draw a line between each set of points that have the same magnetic value) on the map. Stores only the line information needed to draw the lines at the base and interval magnetic values you specified.


When you open the output in ArcMap or ArcCatalog, a line will be drawn that connects all points that have 0 decimal degrees as their declination value; a line will be drawn that connects all points that have 3 decimal degrees as their declination value, then one for all points that have 6, then 9, and so on.

An increment value the tool uses in the isoline interval method. The isoline interval method is one of two methods you can use to generate isolines. Type a numeric value in this field (and one in the base value field) if you want to use this method.

With this method, isolines are drawn based on two values you provide, a base value and an interval value. The base value is the magnetic value for which you want the tool to start generating isolines. The interval value is the increment for which you want the tool to generate lines after it generates the base value line. Technically, the lines aren't actually generated until you open the output in ArcMap or ArcCatalog; but the information to draw the lines is created and stored in the output.

The units for both values are the same as those specified for the magnetic field variable you chose to calculate. Inclination and declination are in decimal degrees. The other variables' units are nano Teslas.

For example, if you chose declination as the magnetic value you want to calculate and provided a base value of 0 and an interval value of 3, the tool:

(1) Takes the input feature class/data you gave and altitude values and computes declination values in decimal degrees for all of the input data.


(2) Creates a set of intermediate rasters in a temporary directory; they are deleted after the tool has finished its computations.


(3) Creates a shapefile named wmmpoint in your C:\Documents and Settings\<user name>\Local Settings\Temp directory and creates a raster named WMMInRaster in the same directory. These items also appear in the ArcMap table of contents if you have ArcMap open.


(4) Creates the information needed to draw isolines (to draw a line between each set of points that have the same magnetic value) on the map. Stores only the line information needed to draw the lines at the base and interval magnetic values you specified.


When you open the output in ArcMap or ArcCatalog, a line will be drawn that connects all points that have 0 decimal degrees as their declination value; a line will be drawn that connects all points that have 3 decimal degrees as their declination value, then one for all points that have 6, then 9, and so on.

A list of magnetic values that the tool uses in the Isoline Value List method to compute how isolines should be drawn. In this method, the tool takes the first magnetic value you provide (the first value in the list) and draws a line connecting all of the points that have the first magnetic value. It takes the second value you provide and draws a line connecting all of the points that have the second magnetic value, and so on until it has drawn a line for every value you provided.

Which magnetic value (variable) the tool uses in its computations is determined by which variable you have selected in the tool's Magnetic Field Parameter drop-down list.