|
Easy Geography Network
Using the geography network in ArcMap seems pretty straightforward. You just find the data you want and click the button, "Add data to Map", right? If you've used Geography Network you know that not everything is that easy. For instance, maybe you've had problems getting your own local data to line up with Geography Network data? In the document below I'll show you a few tricks to make navigating and using 'Map Services' on the Geography Network a lot easier. And if you publish data there is one simple trick for making Map Service registration a little easier too. A list of topics follows:
Search methods
Image Service v Feature Service
Connect directly to Server
Programs you can use to view map services
Overlaying multiple layers
Save data: your options
Make life EASY: GNet template
Registering Maps and Data you Publish
Geography Network Search Methods
As you may already know there are several ways to search the Geography network. The 3 principal methods are through the geographic search (zooming in on smaller and smaller areas from which you want to find data), keyword search (which may be geographic words such as town name or topical keywords such as 'census population'), and category (there is a dropdown box with a list of broad categories). These methods work best if you do them in order. Select a place by using the select box (red box) tool, or type a placename and click Go. If you get placenames on the right panel, select one of them. Selecting a placename only serves to create a new selection box on the left panel (map view). If you click 'Go' again you will not go any farther. You must then click 'select' or type a keyword/choose category and click 'select' to get results. You can also click on the 'Browse' tab and search by publisher.
Image Services vs Feature Services
A map service is a geographic data layer served on the internet via ArcIMS (Internet Map Server). It may exist on the server as a shapefile or a database layer (SDE). That doesn't really matter. What you (the user) see is a map layer. What does matter to you is what type of map service it is. An image service is a snapshot of map layers created by the server. A feature service on the other hand is a layer that you can interact with, manipulate and intermix with other data as you would a shapefile.
Bob Slobodian (our esteemed Director) puts it thus: you visit McDonald's and ask for french fries. Your customer service technician takes your money and hands you a 4x6 glossy photo of french fries. If you're decorating your office with things that make you feel warm and
greasy inside, you walk away happy. If you were actually hungry, or you want to take those fries back to the lab to reverse engineer the secret to flavorful vegetable oil, you will be disappointed. A picture's worth a thousand words but you can't do much with the photo but look at it. An
image service is like the glossy photo. A feature service on the other hand, would be the actual french fries, salt and all. An image service is just a static snapshot (raster) of a map layer(s). You can't change the symbology. You want census tracts to be bright green for high population density? Too bad! With a feature service you can change symbology, do analysis and more (Sorry Bob, I editorialized a bit). Read about overlaying and saving map data to find out more about image versus feature service.
Connect directly to a map server
Once you find a map service that looks interesting, click on the details and scroll down to find out the name of the server. You can also get this information from a map service you have already added to your map document, by right-clicking on the layer and looking at the source information. Once you find the name of the server you can connect to the server directly and possibly find additional map services that are not listed on the Geography Network. How? You click on the add data button, click in the 'look in:' drop down box and select 'Internet Servers'. Double-click 'Add Internet Server'. Type or paste in the server URL. Click OK. Click 'Add' button and you will see a list of all of the map services on that server. Cool, huh?
Programs you can use to view map services
You can use 4 main type of applications to connect with specific map services:
1. ArcExplorer 3.1 (Free, downloadable Java application)
2. ArcMap 9.x+
3. Enabled ArcIMS web applications (developed with Java viewer)
4. Geography Network Explorer (the search tool on GNet website)
The procedure for connecting to map services is almost identical from any of these applications. In this document I refer to ArcMap but you can use the same methods in ArcExplorer, and ArcIMS web sites. In Geography Network Explorer it is a little different but fairly intuitive. Basically you select a service and click 'View map'. You are now connected to the map service. You just can't do much with it from the Geography Network Explorer. It is a browsing tool only.
Overlaying multiple layers
Why is it that when you try to overlay a map service (data from the Geography Network) on top of your own local data you can't see them both? It's probably due to one of two problems: 1) one data source is missing a prj file (coordinate system information), or 2) you have an image service drawing on top of local data and completely covering it up. But don't worry! You can fix both of these problems.
In order to fix the first problem your computer must know the correct coordinate system information for both the internet map service and your local data set. I say your computer must know because what ArcMap needs to line up data from different coordinate systems is a ".prj" file associated with each shapefile. Without the ".prj" file ArcMap won't know what coordinate system your file is in. If you have only one map service or shapefile in your map it may not matter. If you don't have a ".prj" file for your local data you can create one easily with ArcCatalog. For a map service you may have to cheat. If the map service publisher didn't include one, you can set the coordinate system in the data frame properties (right-click on the layer to get to this) to the correct coordinate system. For this you will have to find out the correct coordinate system. You can check the full record on the geography network for that map service and hopefully find the coordinate system information. If this doesn't work you can contact the data originator and ask them (while your at it, remind them politely that it would be nice if they could add a .prj file to their shapefile/map service and make everybody's life easier).
Want to learn more about using projection files? Read our tip sheet on projection with ArcMap.
Save data: your options
When saving map service data you have two options. You can save the map document (.mxd) with layers from the Geography Network. If you do this, every time you open that document, ArcMap will attempt to connect to the host server and get the most recent results from that map service. In other words, if someone is maintaining that data layer you may get a slightly different (more up-to-date) map. It also means that if you can't connect to their server (if their server is down) you are out of luck. The other option only pertains to feature services. You can save the feature service by Right-clicking on data layer..Data..Export Data and saving the data as a shapefile. In fact you can select only the records you want (by query, Select by Attributes, Select by Location, etc..) and just export those as a shapefile. Then add the new shapefile to the map document and delete the original map service layer. Now you will have your own local version of the data from the map service. Note: some map services restrict the number of features you can extract at one time.
Make life EASY: GNet template
Is all of this making your head spin? Just want an easy way to extract data for your area? I may have a solution:
1. Open ArcMap or create a new map document (if it's already open)
2. Add your boundary (city/county/whatever) in your preferred coordinate system.
3. Save the map document as a template (file type=".mxt")
Now you can open ArcMap anytime and create a new document with the template you created. Add any data from the geography network (always put image services on the bottom) and you will quickly find out whether the map service will line up with your data. You can use the boundary file to cutout (Use Selection..Select by Location) feature service data just for your area of interest. Good luck!
Registering Maps and Data you Publish
You can register any kind of geographic product to the Geography Network. The beauty of the Geography Network is the way it lets a desktop GIS user find and connect to live GIS data via map services. But if you have shapefiles on your website or ftp site and you want to list them in the Geography Network catalog, go for it! For shapefiles, click on 'Publish New Record' and set the 'type of content' to 'Geographic Data Set' (first dropdown box).
Filling out all of the fields to describe the data or map service you are registering is a necessary evil. It takes a lot of time, but poor metadata means that fewer users will be able to successfully navigate the catalog to your data. One simple trick is to: Open 2 browser windows when you fill out the registration form. In one window, navigate back to where you can select a record from 'Update Existing Content'. Open the existing record that has the most similarities to your new record and copy and paste entries (using alt+tab or clicking on the start bar to switch between windows) from the existing record into the new one. This can help save a few minutes every time you enter a new record and it will ensure that you use consistent language in your descriptions.
|
