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Site maps of the model region, such as aerial photographs, topographic maps and satellite imagery, are often useful for gaining a perspective of the dimensions of the model, and for locating important characteristics of the model. Although maps do not contain any specific data used in the calculations, and the presence of a map does not influence the results of the simulation, they are useful for enhancing visualization of the model.

Visual MODFLOW Flex supports the following raster graphics file types:

Bitmap (*.BMP)

Tagged Image Format (*.TIF)

JPEG Interchange Format (*.JPG)


Note: When a raster image is imported into Visual MODFLOW Flex, the source file is copied and saved in the project’s data repository folder. As such, the original file may be modified, moved or deleted without affecting the imported raster image.

To import a map into Visual MODFLOW Flex, follow the steps below:


Right-click in the Data Explorer and select Import Data... from the pop-up menu.

Select Map from the Data Type drop down list.

Click the [...] button and locate the source file.

Enter a Name and a Description for the data, and click [Next] to continue

Next, select the Coordinate System of the image file. If the coordinate system is different than the one defined in the project settings, Visual MODFLOW Flex will perform a geotransformation, converting all coordinates to the project’s coordinate system.

Click the [Next] button to continue to the next step.


All raster images must be georeferenced before importing into Visual MODFLOW Flex. If the selected raster image has already been georeferenced, it will have an associated "world" file, and as such, it will not need to be georeferenced in Visual MODFLOW Flex. Please note that this world file must have the same filename as the image, and must be located in the same folder as the selected source file, in order for Visual MODFLOW Flex to recognize it. The following table summarizes the supported graphics file types, and the corresponding georeferencing tag files:


Raster Source

Corresponding World File








If your source image has a world file, you can skip to the final step. If the source file does not have a world file, you will be prompted to manually georeference the raster image. This procedure is described in the following section.


Georeferencing Images

Georeferencing a graphics file involves mapping a coordinate system to the individual pixels of the image. When this is required, the following window will display, when importing a raster image:



Toolbar Buttons

The buttons in the top toolbar are described below:

Save: Saves the transformed image, along with a corresponding georeferencing tag file.

Zoom In: Click-and-drag the mouse to select the zoom area.

Zoom Out: Zoom out of the image.

Full Extent: Zoom completely out so that the entire image is shown.

Pan: When zoomed in, move the image left, right, up or down.

Add (Control Point): Add a georeference point. See "Adding Georeference Points".

Delete (Control Point): Delete a selected georeference point.

Transform Image: Assigns coordinates to image pixels using the specified control points.


Output Region: This button allows you to save a specified area of the image to the georeferenced file, after the image has been transformed. By default, the output region is the whole image. Click-and-drag a rectangular box on the image to define a new output region, and then click the Save button to save the output region to the georeference file.

Configure Georeferencing Options: Opens the configure georeferencing options dialog box. For more information on these options, please see "Configure Georeferencing Options" section.

Magnification Selector: Select a magnification level from the combo box.


Control Points Table

The control points table contains the specified control points. You can edit an existing control point by selecting the point from the table, and then clicking the  Edit button. A dialog box will display prompting you to modify the control point coordinates.

You can also delete a control point from the control points table. To do so, select an existing control point from the grid, and then click the  Delete button.


Georeference Information Table

The georeference information table displays information about the georeferenced image including the original image file name and path, the original image size, and coordinate type (projected, local or geographic). It also displays information on the transformation such as the degree of rotation, scale X-Y shift, and the output file name path and image size.



Adding Georeference Points

In order to map pixels of the image to a coordinate system, the image must have at least two georeference points with known world coordinates.  To set a georeference point:

From the top toolbar, click on the  Add button.

Click on a map location where the world coordinates are known.

A georeference point window will appear prompting for the X and Y world coordinates of the selected location.

Enter the X and Y coordinates for this point.

Repeat this procedure for additional georeference points.

When you set a georeference point, it is added to the Control Points Table.


You can improve the accuracy of the georeferencing by adding more than two control points to the image. When the image is transformed, the Preview tab will display the original control points and the corresponding georeferenced points, thus allowing you to visualize the accuracy of the georeferencing.

Once you have set at least two georeference points, click the  Transform button to georeference the image. The georeferenced image will then be displayed in the Preview tab.


Editing Georeference Points

To edit a georeference point:

Select the georeference point from the Control Points Table

Once selected, click the  Edit button (located just beneath the control points table)

A Georeference point window will appear prompting for the X and Y world coordinates of the selected location.

Enter the new X and/or Y coordinates for this point.

Click the [Ok] button.


Note: You must click the Transform button again in order for the georeferencing to update to reflect the modified X-Y values.


Deleting Georeference Points

To delete a georeference point:


Select the georeference point from the Control Points Table.

Once selected, click the  Delete button (located just beneath the control points table)


Configure Georeferencing Options

When the  Configure Georeferencing Options button is selected, the following dialog will open:



Symbols Tab

This tab allows you to change the style settings of the original control points and the georeference points. Choose a Style, symbol Size and Color. A preview of the symbol settings is shown in the boxes below.


Georeference Image Tab

This tab allows you to define settings for the georeferenced image. Each setting is described below.


When a georeferenced image is rotated, you can fill the areas of empty space with a specified color. Otherwise, leave the check box unchecked and the empty space will show transparent.

Click the color box beside Fill color for empty area to select the color to fill the empty spaces (only if Show Fill Color option is selected).

Use the slider to set the JPEG Image Quality. When set closer to L (low), more compression is used in the saved georeference image file, resulting in a smaller file and poorer quality. When set close to H (high), less compression is used in the saved georeferenced image file, resulting in a larger file with better quality.

From the Interpolation Mode combo box, specify the interpolation method (algorithm) to use when the image is scaled or rotated The various interpolation methods are briefly described below. Keep in mind, lower-quality interpolation mode will result in a smaller output file, whereas high-quality interpolation modes will result in a larger output file.

Default: default interpolation mode.

LowQuality: a low-quality mode.

HighQuality: a high-quality mode.

Bilinear: Bilinear interpolation. No prefiltering is done. This mode is not suitable for shrinking an image below 50 percent of its original size.

Bicubic: Bicubic interpolation. No prefiltering is done. This mode is not suitable for shrinking an image below 25 percent of its original size.

NearestNeighbor: Nearest-neighbor interpolation.

HighQualityBilinear: Specifies high-quality, bilinear interpolation. Prefiltering is performed to ensure high-quality shrinking.

HighQualityBicubic: High-quality, bicubic interpolation. Prefiltering is performed to ensure high-quality shrinking. This mode produces the highest quality transformed images.


Graticule Tab

The graticule tab provides display options for the preview graticule. These settings are described below.


Padding Space Controls the amount of buffer space between the edge of the preview window display, and the labels on the axis. It may be necessary to increase this value when the X and Y coordinates contain many digits.

Line Style Select from various line styles, e.g., solid, dashed, etc.

Line Color Set the color of the graticule lines.

Back color Set the background color of the graticule.

Major mark width Set the width of the major mark ticks.

Minor tick distance Set the distance between minor ticks.

Auto Interval Automatically calculates the distance between graticule lines.

Interval If Auto Interval is not selected, set the distance between graticule lines.

Mark Settings Controls the axis labels. For each axis, you can set the visible status, rotate the label, and control the gap between the label and the axis itself.

The final step involves previewing the raster image and viewing coordinate information, before importing into Visual MODFLOW Flex.



The Map Coordinates frame provides the georeferenced coordinates of the Top Right and Bottom Left corners of the image. The path of the georeferenced image, and the associated georeference tag file is also shown.

Click the [Finish] button to import the map into Visual MODFLOW Flex.





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