Minnesota Geographic Data Clearinghouse Data Delivery Service

 

 

The Minnesota Clearinghouse Data Delivery Service allows you to choose geographic themes, choose a spatial area of interest, and extract data for those themes for just your area of interest. This site is envisioned primarily as a data distribution tool rather than as a mapping tool. The on-screen mapping capability, along with the associated data documentation, allows you to preview the data and decide whether the data is appropriate for your planned use. Several data delivery map services are planned, each supporting a different category of data (for example, boundaries, hydrography, soils and land use.) The Data Delivery Service page is made up of a number of features:

 

The Map View Screen enables you to preview the data themes and decide what you wish to download. Use the Theme Layer List to the right of the map view screen to specify which layers you want to draw. Use the tool buttons in the lower left corner of the screen to pan and zoom within the map, and to query map layers. A default theme is on display when the user first enters the application.

 

The Theme Layer List enables you to specify which map themes you wish to draw in the map view screen. The Theme Layer List includes three boxes, each of which contains an identical pulldown list of data layers available for this theme. You may pick a different theme in each box, and display up to three themes. If you wish to display a theme, highlight the theme in one of the boxes and check the visible checkbox to the left of the theme name. If you wish to query on a theme, check the active button to the left of the theme name.

 

·         The Visible checkbox indicates which themes the user wishes to see the next time the map is redrawn. Multiple theme can be checked to be visible at the same time. ( Some combinations of theme may be more difficult to distinguish than others when they are displayed simultaneously.) Important Note: Some data themes, such as wells, minor watersheds, minor roads, imagery, etc., are very dense and would not display well as a statewide extent within the map view screen. These themes are set up to be scale-dependent that is, as a certain scale, as appropriate for the data set, these map themes become visible on the screen.

 

·         The Active button can be used to indicate one of the map themes. This theme, once designated as active, can be queried for instance, you can then use the identify button to find out information about a specific feature, or use the query button to select features based on characteristics of that theme. Only one theme can be active at a time.

 

·         The Metadata button provides documentation, or metadata, for the map theme. Metadata describes the origin, purpose, scale, attributes, and creation methodology of the data set. It is another tool to help you evaluate whether this data set is appropriate for your purposes. This metadata is created according to the Minnesota Geographic Metadata Guidelines (MGMG).

 

The Refresh button redraws the map view screen with the current set of visible themes as specified by the user.

 

A Legend appears below the theme list referencing all the themes chosen by the user. This legend area will include a scrollbar if the legend length exceeds the available screen size.

 

The Tool Buttons are displayed in the lower left hand corner of the screen. Tools available to the user include:

 

Zoom In - Zoom into the map to show a smaller area. After clicking the zoom in button, draw a rectangular box on the map viewing screen with your mouse. The map area will automatically be redrawn to match the areal extent that you indicated. At a smaller areal extent, more layers may become visible on the screen.

 

Zoom Out Zoom out of the map viewing screen to show a larger area. The actual extent of the zoom is determined by the system. You can, however, indicate with the mouse the point from which you wish to zoom out.

 

Identify Use this button to find out more about particular features within a map theme. This option only works on the Active layer, so first indicate which theme you wish to make active. Once you have clicked the Identify button, move the mouse to the map feature you want more information about. The application will return information about the feature from the files feature attribute table. This information is displayed in the lower right-hand corner of the screen.

 

Pan Use this button to move around on the map to display different areas of the map at the scale you have chosen. Place the cursor at a point within the map view screen, and drag the mouse to pan the screen.

 

Download - Use this button to download data. All data sets are in ArcView shapefile format. When the download button is activated, the application will clip all data themes checked as visible to the areal map extent displayed on the screen, then zip all data together and begin a download routine which will ask you where you want to store the data on your local machine. The data set downloaded is a zipped file containing shapefiles of all of the selected layers for the area of interest. Note: The clip option used will include all polygons which are partially contained within the bounding box. If the polygons were actually clipped to coincide with the bounding box, then some attribute information associated with the clipped polygons might be corrupted.

 

Overview This option activates an overview map of the state, highlighting the area selected. This overview map appears in the upper left-hand corner of the screen.

 

Full Extent This option brings you back to the full extent of the map i.e., the entire state.

 

Last Extent This option brings you back to the previous areal view of the data, before your last zoom in. This option can be used multiple times.

 

Query This option only works on the theme which is chosen as active. Activate the query tool button to build a query based on attributes of the data set for example, all lakes with areas greater than 50 acres and draw only those features to the map when a refresh is done.

 

When you activate the query tool, an entry screen appears in the lower right corner of the screen. This entry screen consists of text boxes and buttons to help you contruct the query. In the Field textbox, enter the data field on which the query should be based. A pulldown list will list all data fields from the layers attribute table. Highlight the field which will be used to make the query. Then choose an operator from the Operator Textbox pulldown list. (Operators include =, >, <, >=, <=, and LIKE). Then input the value for the feature into the Value textbox. (Character features need to be inside quotation marks). A Sample List of values is available by activating the Sample Values button. This retrieves the first 50 records from the database and lists their values in a pulldown list. Because of the size of these databases, this generally represents just a small subset of the values available. When you have typed in or selected a value, hit the Add to Query String button. You may extend the query by hitting the Boolean buttons to the far right of the query area (And, Or, Not, (, ). Then you can add another query. When you have completed all query entries, hit the Execute button to begin the query.

 

When the query has been completed, several things will happen. The selected features are highlighted in yellow in the map view screen. The attributes of the selected features are listed in the right-hand corner of the screen. An option appears to Zoom to Selected Records. Pushing this button zooms the map view screen in to encompass just the selected features.