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NMPlot User's Guide, Chapter 14: Background Map Formats

NMPlot can display background map layers stored in the following Geographic Information System (GIS) formats.

This chapter discusses each of these formats in detail.

See Background Layers for instructions on adding background map layers to a plot.

ARC/INFO Shapefile (SHP)

Shapefile Map Layer Options Dialog Box

Use the Shapefile Map Layer Options dialog box to configure a shapefile map background layer.

The Shapefile Map Layer Options dialog box is a Multiple Page dialog box. See Multiple Page Dialog Boxes for more information.

Shapefile Name Options Page

Use the Shapefile Name page of the Shapefile Map Layer Options dialog box to set the name of the shapefile you wish to display.

Type the name of the file containing the shapefile. Press the Browse button , located to the right of the text box, to display the Open File dialog box, which allows you to browse for the file.

Note:

A single shapefile actually consists of three files: a main file, an index file, and an attribute file. These files should have the extensions .shp, .shx, and .dbf, respectively. On the Shapefile Name page, specify the name of the main file (i.e., the .shp file).

Coordinate System Options Page

Use the Coordinate System page of the Shapefile Map Layer Options dialog box to specify the coordinate system used by the shapefile.

See Coordinate System Control for instructions on specifying a coordinate system.

Scale Options Page

Use the Scale page of the Shapefile Map Layer Options dialog box to specify the scales at which this shapefile is displayed.

If a plot is displayed at a scale below the one you specify, the shapefile layer is not displayed. This is useful if you have shapefiles with varying levels of detail. Using multiple shapefiles, you can construct maps that reveal more detail as you zoom in.

For example, assume that you have two shapefiles. The first contains main roads, and the second contains secondary roads. You can set the main roads layer to display at all scales, and the secondary roads layer to display only at scales above 1:24,000. This prevents the secondary roads from cluttering the plot if you view it at a smaller scale.

Drawing Options Page

Use the Drawing page of the Shapefile Map Layer Options dialog box to specify the style (colors, line widths, etc.) used to draw features in the shapefile.

You can set the following options.

Technical Details

NMPlot can display shapefile records of the following types.

Shapefiles containing a mixture of record types are supported.

Only the Main (.shp) file is required. The Index (.shx) and Attribute (.dbf) files may be present, but are not used. Attributes are not loaded.

The shapefile format is controlled by Environmental Systems Research Institute, Inc (ESRI), the makers of the ARC/INFO GIS system. The official specifications are documented in an ESRI white paper titled "ESRI Shapefile Technical Description", which can be found on the ESRI web site, http://www.esri.com . As of September 2000, the URL for this document was http://www.esri.com/library/whitepapers/pdfs/shapefile.pdf.

Digital Line Graph (DLG)

Map Formatting Schemes

Every map feature in a Digital Line Graph (DLG) file contains attribute codes that specify properties of the feature. For example, a line feature might have the attribute codes for Primary Road and Under Construction. An attribute code consists of two integers: a 3-digit major code, and a 3- or 4-digit minor code. Attribute codes are standardized and documented: see Technical Details.

A map formatting scheme is a file containing rules that associate attribute codes with display styles. For example, a rule might state that line features with the code 170 212 (four-wheel-drive roads) should be drawn in a thin gray dashed line.

Map formatting schemes are stored in files with the extension .mapformattingscheme. You can create, view, and edit map formatting schemes using NMPlot.

To open an existing scheme, choose Open from the NMPlot File menu, then select a map formatting scheme file. A map formatting scheme document window appears.

Map formatting scheme rules are divided into three groups, according to whether they apply to point, line, or area map features. Press one of the buttons to edit a group's rules. For example, if you press the Edit Line Rules button, a dialog box appears that allows you to edit the rules used for line features.

The rules in a map formatting scheme are very similar to the display rules used for grid geographic annotations. Please review Displaying Geographic Annotations, which describes display rules and discusses how they are edited. Map Formatting Scheme rules are edited in the same fashion, with three exceptions.

  1. Map Formatting Scheme rule tables have an additional column labeled Rule Name. This column is used to give a descriptive name to a rule.

  2. Instead of columns labeled Category and Name, map formatting scheme rule tables have a column labeled DLG Attribute Codes. Map Formatting Scheme rules are matched against a DLG feature's attribute codes in the same way that Grid Geographic Annotation display rules are matched against an annotation's category and name. In the DLG Attribute Codes column, type the attribute codes associated with each rule. Here are some examples.

    • "170 201" matches DLG features with the attribute code 170 201.

    • "170 201..205" matches DLG features with a major code of 170, and a minor code between 201 and 205.

    • "170 201,203" matches DLG features with a major code of 170, and a minor code of either 201 or 203.

    • "170 201 and 170 603" matches DLG features with both attribute codes 170 201 and 170 603.

    • "170 201 then 170 603" matches DLG feature with both attribute codes 170 201 and 170 603, with 170 603 following 170 201 in the feature's list of codes.

    • " " matches DLG features with no attribute codes.

    As an example, "170 201-208 and 170 603,604" matches all primary and secondary roads under construction.

  3. Map Formatting Scheme rule tables have an additional column labeled Scale (1:x). This column allows you to specify the minimum scale at which matching DLG features are displayed. If a plot is displayed at a scale below a rule's scale, any DLG features matching that rule are not displayed. This allows you to construct maps that reveal more detail as you zoom in.

Note:

NMPlot is distributed with a default map formatting scheme. This scheme is in the file Default.MapFormattingScheme, which can be found in the directory where NMPlot is installed.

Note:

This section provides only the briefest introduction to attribute codes. If you intend to modify map formatting schemes, obtain the official DLG documentation, which describes attribute codes in detail. See Technical Details for information on obtaining the documentation.

Digital Line Graph (DLG) Options Dialog Box

Use the Digital Line Graph Map Layer Options dialog box to configure a DLG map background layer.

Descriptive name of this map layer: Type a short description of this map layer. Examples are "Roads" and "Water Features". This allows you to identify this layer in the future.

Map formatting scheme that will be used to interpret this map layer's data: Type the name of the file containing the map formatting scheme used to display this DLG layer. Press the Browse button , located to the right of the text box, to display the Open File dialog box, which allows you to browse for the file. Map formatting schemes typically have the extension .mapformattingscheme. See Map Formatting Schemes.

Geographic datum used to store coordinates in this map layer's DLG file(s): Select the DLG files' geographic datum. See Datum Control for information on selecting datums. See Introduction to Datums for general information on datums.

Important:

Many DLG files supplied by the United States Geological Survey (USGS) are in the North American Datum of 1927 (NAD-27). Make sure that you know the correct datum for your DLG files.

Show Points, Lines, Areas: Check the boxes corresponding to the geographic features you wish to display. Typically, all three boxes should be checked. However, if necessary, you can restrict which features are displayed. For example, you can choose to display only point geographic features.

Name(s) of DLG file(s) that contain this map layer's data: Type the names of the DLG files that you wish to display as part of this layer. Any number of files can be listed. Press one of the Browse buttons , which are located to the right of the file name text boxes, to display the Open File dialog box, which allows you to browse for a file. DLG files typically have the extension .dlg.

Press the Add File To List button to add a file. Remove a file by clicking on it with the mouse, and then pressing the Remove File From List button.

Technical Details

NMPlot can read 1:24000 and 1:100000, level 3, optional format DLG files.

The coordinate system of the DLG file must be Universal Transverse Mercator (UTM).

The DLG file cannot contain DLG accuracy records.

NMPlot can display DLG records of the following types.

DLG files containing a mixture of record types are supported.

NMPlot can merge DLG topology data in layers containing more than one DLG file.

The DLG format is controlled by the National Mapping Division of the United States Geological Survey (USGS). The official specifications are documented in a technical report titled "Standards for Digital Line Graphs", which can be found on the USGS web site, http://www.usgs.gov. As of September 2000, the URL for this document was http://rockyweb.cr.usgs.gov/nmpstds/dlgstds.html. This document contains a list of all DLG attribute codes.

AutoCAD Data Exchange Format (DXF)

Warning:

Use the DXF format as a last resort, only if no alternative is available. DXF is a very ambiguous format, which results in different applications interpreting the same DXF file in different ways. You can expect fewer problems using other formats, such as ARC/INFO Shapefile or Digital Line Graph.

DXF Map Layer Options Dialog Box

Use the DXF Map Layer Options dialog box to configure a DXF map background layer.

The DXF Map Layer Options dialog box is a Multiple Page dialog box. See Multiple Page Dialog Boxes for more information.

DXF Filename Options Page

Use the DXF Filename page of the DXF Map Layer Options dialog box to set the name of the DXF file you wish to display.

Type the name of the DXF file. Press the Browse button , located to the right of the text box, to display the Open File dialog box, which allows you to browse for the file. This file will typically have the extension .dxf.

Coordinate System Options Page

Use the Coordinate System page of the DXF Map Layer Options dialog box to specify the coordinate system used by the DXF file.

See Coordinate System Control for instructions on specifying a coordinate system.

Scale Options Page

Use the Scale page of the DXF Map Layer Options dialog box to specify the scales at which this DXF file is displayed.

If a plot is displayed at a scale below the one you specify, the DXF layer is not displayed. This is useful if you have DXF files with varying levels of detail. Using multiple DXF files, you can construct maps that reveal more detail as you zoom in.

For example, assume that you have two DXF files. The first contains main roads, and the second contains secondary roads. You can set the main roads layer to display at all scales, and the secondary roads layer to display only at scales above 1:24,000. This prevents the secondary roads from cluttering the plot if you view it at a smaller scale.

Drawing Options Page

Use the Drawing page of the DXF Map Layer Options dialog box to specify the style (colors, line widths, etc.) used to draw features in the DXF file.

You can set the following options.

Technical Details

NMPlot can display DXF entities of the following types.

NMPlot recognizes entities in either BLOCKS or ENTITIES sections.

The DXF format is controlled by Autodesk, Inc., the makers of AutoCAD. The official specifications are documented in an appendix of the AutoCAD Reference Manual.

Georeferenced Bitmap

Georeferenced Bitmap Map Layer Options Dialog Box

Use the Georeferenced Bitmap Map Layer Options dialog box to configure a Georeferenced Bitmap Image map background layer.

The Georeferenced Bitmap Map Layer Options dialog box is a Multiple Page dialog box. See Multiple Page Dialog Boxes for more information.

Image File Options Page

Use the Image File page of the Georeferenced Bitmap Map Layer Options dialog box to set the name of the bitmap image file you wish to display.

Type the name of the bitmap image file. Press the Browse button , located to the right of the text box, to display the Open File dialog box, which allows you to browse for the file.

NMPlot can read the following types of bitmap image files.

Georeferencing Options Page

Use the Georeferencing page of the Georeferenced Bitmap Map Layer Options dialog box to specify the portion of the Earth's surface represented by the bitmap image.

Image projection coordinate system: Select the projection coordinate system of the bitmap image. See Coordinate System Control for information on specifying a coordinate system.

Image georeferencing: Use the drop-down list to select the method for georeferencing the image. You have three choices.

Note:

You should be able to find georeferencing information in the documentation that accompanies your bitmap image. If you do not have this information, ask the person or organization who supplied the image. Or, contact your local GIS expert. If NMPlot does not support your image's projection, contact the developers: see Contacting Wasmer Consulting.

Georeferenced bitmap images are often distributed with an accompanying world file, which contains georeferencing information. However, keep in mind that a world file does not contain information about an image's projection. Your image's projection must be entered into NMPlot by hand.

Caution:

You can display any number of georeferenced images on a single plot. However, all of the images must have compatible projection coordinate systems. NMPlot will allow you to create a plot with images in different projections, but this should be attempted only if you have a thorough understanding of map projections. To be safe, novices should insure that all georeferenced images have exactly the same projection.

Technical Details

NMPlot can read bitmap images in the following formats.

Compressed ARC Digitized Raster Graphics (CADRG)

Compressed ARC Digitized Raster Graphics (CADRG) Map Layer Options Dialog Box

Use the Compressed ARC Digitized Raster Graphics (CADRG) Map Layer Options dialog box to configure a CADRG map background layer.

Table of contents file: Type the name of the CADRG table of contents file. Press the Browse button , located to the right of the text box, to display the Open File dialog box, which allows you to browse for the file.

The CADRG table of contents is a file is named A.TOC. You will find it in the root directory (i.e., a directory named RPF) of the CADRG map you wish to load.

Brightness adjustment:
Contrast adjustment: Type numbers between -100 and 100 to indicate how much the brightness and contrast of the CADRG map should be adjusted before it is displayed. Values of 0 leave the map unchanged. Values above 0 increase the brightness and contrast; value below 0 decrease the brightness and contrast.

Longitude Tweak:
Latitude Tweak: Type numbers between -0.1 and 0.1 to indicate how much the CADRG map should be shifted in degrees longitude and latitude. If foreground elements do not line up exactly with the background CADRG map, use non-zero values to shift the map slightly. The appropriate tweak values are best found using trial and error.

Tip:

As distributed, most CADRG maps are poor backgrounds. The map colors are too intense, making it difficult to see any foreground detail displayed over the map.

In most situations, you should adjust the brightness and contrast so that the map colors are muted. As a starting point, try a brightness adjustment of 30 and a contrast adjustment of -70. These values have been found to work well with most CADRG maps distributed by the United States' National Imagery and Mapping Agency.

Tip:

CADRG maps are typically distributed on a CD-ROM. If desired, you can copy the CADRG map to your hard drive. Simply copy the RPF directory, taking care to preserve the subdirectory structure.

A CADRG map will load much faster from a hard drive. It may also be more convenient to use, since you do not have to insert a CD-ROM.

Warning:

CADRG maps can be huge. Uncompressed, they can be several thousand megabytes in size. NMPlot supports incremental loading: it reads sections of the CADRG map on an as-needed basis. However, as you zoom out on a plot, you cause more CADRG map data to be loaded. If you zoom out far enough, enough map data can be loaded to overwhelm even the largest computer.

Note:

Do not confuse the Compressed ARC Digitized Raster Graphics (CADRG) format with the Digital Raster Graphics (DRG) format developed by the United States Geological Survey. They are different formats.

Technical Details

Compressed ARC Digitized Raster Graphics (CADRG) is a georeferenced bitmap format for storing background maps. It was developed by the United States Department of Defense's Defense Mapping Agency (now known as NIMA, the National Imagery and Mapping Agency).

The CADRG format is documented in military specification MIL-PRF-89038 (formerly MIL-C-89038), dated 6 October 1994, and Amendment 1, dated 27 April 1999. These documents can be downloaded from the NIMA web site, http://www.nima.mil/. As of September 2001, the URLs for PDF versions of these documents were http://www.nima.mil/publications/specs/printed/89038/89038_CADRG.pdf and http://www.nima.mil/publications/specs/printed/89038/89038_A1.pdf.

SlippyMap

SlippyMap is a standard for accessing map data via the internet. Maps are transmitted as bitmap image tiles that are downloaded on an as-needed basis.

Numerous SlippyMap servers on the internet are available that supply maps in a variety of styles. Some servers are supported by donations and supply their maps for free with no restrictions. Others require acknowledgment and/or a paid subscription.

Important:

SlippyMap providers can and do enforce restrictions on how their map data is used. Using SlippyMap data in a manner that does not meet the provider's restrictions is a violation of law, and can results in legal liabilities. You are responsible for determining a providers restrictions and abiding by them.

SlippyMap Map Layer Options Dialog Box

Use the SlippyMap Map Layer Options dialog box to configure a SlippyMap background layer.

Tile Server URL Prefix:
Tile Addressing Scheme:
Tile Server URL Suffix: Each SlippyMap tile image is accessed by a URL (i.e., an internet address) that encodes the server location and parameters, along with the tile's zoom level and geographic location. Each SlippyMap server will document their URL format. Tile Addressing Scheme is the format used to describe the tile's zoom level and geographic location. Tile Server URL Prefix and Tile Server URL Suffix are the text of the URL before and after the addressing scheme. Note that the text "http:\\" and "\" will automatically be added before/after the URL prefix.

Tip:

If NMPlot is downloading and displaying SlippyMap data, but the resultant maps appears scrambled, it is likely that the incorrect tile addressing scheme has been selected. If you have tried all available schemes and the map still appears scrambled, it is possible that the SlippyMap server is using an addressing scheme that is not currently supported. In this case, contact NMPlot's developers: see Contacting Wasmer Consulting.

Sample Tile URL: An example tile URL, constructed using the URL prefix, addressing scheme, and suffix, is displayed. Press the "Copy Sample Tile URL" button to copy the sample URL to the clipboard. If everything is configured correctly, you should be able to paste the URL into a web browser and have it download and display the tile image.

Zoom Level Range: In the SlippyMap standard, the scale of a map is denoted by an integer zoom level. At zoom level 0, the map displays the entire world, while at zoom level 18, individual houses are visible. Most SlippyMap servers supply maps at zoom levels from 0 to 18, although a few are limited to a different zoom range. By specifying a server's zoom level range, you prevent NMPlot from needlessly trying to download map tiles at zoom levels that the server does not supply.

Attribution Text: The terms of use for some SlippyMap servers require you to display copyright and attribution information when using their maps. Text you enter in the Attribution Text box will be displayed in the lower-right corner of the map by NMPlot.

Attribution Logo: In addition to attribution text, some servers also require you to display a graphical company logo. In this case, the SlippyMap server documentation will supply you with a logo image file that you can download to your computer. Enter the full path file name of this logo image in the Attribution Logo box. It will be displayed next to the attribution text in the lower-right corner of the map.

Presets: Once you have configured the parameters of a SlippyMap server, you can save those settings as a preset that can be accessed in the future. To create a new preset, edit the SlippyMap server parameters as desired, then press the Save as New Preset button. You will be prompted for a name for the new preset.

If you edit the parameters of an existing preset, press the Update Preset button to update the preset with the new settings. Press the Rename Preset and Delete Preset buttons to rename and delete the preset currently displayed in the drop-down preset list.

Show map only at SlippyMap zoom levels: NMPlot can display a SlippyMap at any map scale; data from the closest SlippyMap zoom level is used. However, SlippyMap maps are designed to be displayed with an exact 1:1 correspondence between a map tile image's pixels and your computer monitor's pixels. Displaying them at other map scales can result in reduced legibility.

If the "Show map only at SlippyMap zoom levels" box is checked, then when displaying maps that include SlippyMap data, NMPlot will only display them at the exact scales corresponding to SlippyMap zoom levels.

Note that this setting is a global application-wide option.

Show SlippyMap debug data: If this box is checked, information about the status of the SlippyMap map layer will be displayed in the lower-left corner of the map. Data displayed includes the map's current zoom level and the number of SlippyMap tiles currently being downloaded.

Note that this setting is a global application-wide option.

Technical Details

NMPlot can display SlippyMap tile images delivered in either .png or .jpg format.

SlippyMap maps use the Web Mercator map projection.

Downloaded SlippyMap map tile images are cached on your hard drive for reuse. This greatly increases performance, as the map data for a particular region and zoom level only needs to be downloaded once. To prevent the disk cache from growing too large, the map tile files will be deleted approximately two weeks after they are downloaded. See Cache Options, for more information.


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