DOC

Bringing data into ArcMap - jenster

By Jim Rogers,2014-11-05 21:31
5 views 0
Bringing data into ArcMap - jenster

    Bringing data into ArcMap

In this exercise you will:

    ; Learn how to bring databases into ArcMap

    ; Learn how to add XY data to a map

Adding data to your map

OK, so now you’re a bit familiar with bringing a map into ArcMap and altering some of its appearances.

    It’s time to take this one step further and learn how we can use this to analyze data. We’re going to do something that you should be familiar with from database managers we’ll join tables.

    Keep in mind that most of the time your map file does not come with data like the ones in the first examples did. Most of the time, you’ll have to add your data to your map.

Begin a new document by clicking on this icon:

Let’s add a St. Louis census tract map that does not yet have the demographic data in it. Click the ADD

    DATA icon and add the file called tgr29510trt00.shp. This seems like really complicated file name, but census files often have this sort of naming convention to help you keep things organized. The file is a TIGER file (a standard census mapping file) for Missouri (state code 29) for St. Louis (county code 510). It is a tract file (trt) for 2000 (00).

    Set your data frame properties let’s use State Plane Missouri East as our projection. Let’s use feet as our units.

Right click on the item file and

    view the attribute table. You’ll

    see that it only contains the

    geography information, but

    contains no data.

We’ll need to add another file

    that contains demographic data.

    Click ADD DATA and look for

    the file called

    tgr29000sf1trt.dbf. This is just

    the data, with no geography

    attached to it. You’ll notice in

    your layer window that you

now have a geography and a database:

But right now, they have no association. So we need to dump the data into the geography. I like to think

    of this as pouring our data into our JELLO mold map.

    To do that, right click on the census tracts file in the layers

    window and choose JOINS AND RELATES, then click on

    JOIN.

    It’s important to remember that to join data to a map, you

    need to right click on the geography file, rather than the data

    file.

Next, you’ll get this menu:

    The first drop-down menu will ask what sort of join you

    want to do. In this case, you want to join data or

    attributes from a table.

The next box will ask which field you want to join on in

    the geography or layer file. This is usually the numeric

    code for the census track, block or other geography. In

    our case, its called STFID.

The next box will ask you for the table you want to join.

    In this case, we have only one table. But as you build

    larger maps with more data, you may have several

    options here.

Next, ArcMap needs to know what the join field will be

    in the data. In this case, they happen to have the same

    name STFID but that won’t always be the case. They

    do, however, need to be the same size and format.

ArcMap will ask if you want to index the join fields (This is new to ArcMap 9.0.) Click yes this will

    speed things up. Keep in mind this edits the data, so you won’t be able to do this if you’re working off read-only files.

    Click OK and ArcMap will pour your data into your map. To double check, right click on the census tract layer and look at the attribute table.

    Now let’s look deeper at our map. Remember how we edited the symbology so we could see the tracts more clearly? Let’s do something that’s more likely to help us with stories. Double-click on the tracts

    layer and go to the symbology tab. Click on QUANTITIES in the left window. This is where we can do a map based on some sort of demographic. Let’s start off with population. (POP2000) ArcMap will then

    divide St. Louis’ census tracts into five categories, lumping tracts with similar total population into the same category. It will make calculations on how to divide the tracts into five categories (we’ll look closer at that later on). Click apply, then OK, then look at your map.

    Once you’ve done that map, let’s get more practice before moving on. Look at the totals for each racial and ethnic category, and look at your map as you go along. This is the foundation for many maps that make it into print and on air.

    Before you go on, once again be sure to save your map document just like you did earlier. You may call it anything you like.

Running Rates

    You’ve looked at total population, and each racial and ethnic category. Let’s start putting them together. Go back to properties for your census tracts, click on the symbology tab. Pick QUANTITIES and graduated color from the left-hand box. Under your value field pick a race or ethnicity. Let’s say Black. Instead of just running this map again, let’s take one more step. Notice the box below that says NORMALIZATION. So far we’ve been leaving it blank, as we’ve gotten more familiar with ArcMap.

    Now let’s pick a category.

    Let’s choose POP2000. This

    is the same as doing the math,

    tract-by- tract, of the blacks

    divided by the total population

    within each tract. Apply this

    map and look at it.

    Now let’s do more. You can

    do ratios, such as blacks

    versus whites. Or you can

    divide population by area, to

    see the density in tracts. Or

    you can see, say the blacks in

    each tract as a percentage of

    all the blacks in St. Louis.

Practice exercise

    Use the shape file grunnkrets.shp and add the data in the file grundata.dbf

    Join the data to the map and do another map of your choice.

Mapping dams

    Let’s start a new map. Bring in a map of the United States by opening the file called Counties.shp. Take a look at what’s in this file by viewing the attribute table. Make a map that gives each state a different color.

Be sure to set your map frame properties. Let’s use UTM zone 16 and use miles as our units.

Zoom into Tennessee.

To zoom back to the full map, choose VIEW|ZOOM DATA|FULL EXTENT.

Let’s review how we can categorize information. Double-click on STATES in the table of contents. Go

    to the SYMBOLOGY tab. Click QUANTITIES so we can do a color-coded map by a value in our data. Choose Median_val (median home value) Click apply and now we can see the states more clearly. Then click OK.

Experiment with different category breaks and colors. Save this map (call it TENNESSEE.

Adding Maps On Top Of Maps

    Now let’s add some maps on top of our counties map.

Click the add themes button and pick rivers. Do it again for lakes. And then for city. Remember, you

    need to click the check box in the table of contents to make ArcMap show the map in your view.

Most of the maps you’ve worked with so far contained polygons – or areas. Maps also can contain

    points (such as the cities) or lines (such as the rivers).

    If you’d like to edit the color of

    the rivers so you can see them

    better, double-click on the

    rivers map. Go to the

    SYMBOLOGY tab and double-

    click the symbol box.

You’ll get the symbol selector.

    You can choose one of

    ArcMap’s preset styles for layer type or you can change the

    color and width manually in the

    OPTIONS box.

Let’s go with ArcMap’s river

    symbol by clicking on the

    RIVER symbol in the symbol

    selector. Now do the same with

    the lakes map. Pick a different

    color for the lakes. Now pick

    city. Things get a little crazy

    when you add too many maps. The dots for all those towns obliterate almost all of our map if we are trying to see the whole United States. We could zoom in close to a region so we can make some sense out of all those cities. For now, though, let’s not see that theme. Click

    on the city box to remove the check mark.

Mapping Something That Wasn’t A Map

    We’ve added maps on top of maps. Sometimes you may want to use a file that was never a map to begin with. On rare occasions, a database will contain geographic information within the database. A good example of such a database is the National Inventory of Dams database. We’re going to use federal dam data for Tennessee. It comes in a dBase file, not in a map.

Click the ADD DATA button then find nid_tn.dbf. You won’t see this data in the table of contents.

    Click on the SOURCE button in the lower left-hand corner of the window, and you’ll see the file has

    been added. Now we need to tell ArcMap to add it to the map.

We’ve brought in the table. But we can’t join it like we did with the census data. It does not have a

    census tract number or anything like that. What it does have, however, is a latitude and longitude field. Once ArcMap knows that this data contains a latitude and longitude, it can display it on the map.

    To do that, choose TOOLS|ADD XY DATA:

    You’ll get a dialog box that will ask you which table you want to map

    and which fields contain the latitude and longitude. For the dams data,

    the longitude field is called LONGITUD_X and the latitude field is

    called LATITUDE_Y:

    Click OK. You’ve just transformed a database into a map layer. Edit the dam symbol to something that’s clear. For this exercise, let’s make the dams red dots at about size 8 points. You might notice that ArcMap has a symbol for a dam, but when you add several of them to a map, they are a little hard to see. Feel free to explore the symbols and find one you like.

Click your city map back on and make those 10-point gray pushpins.

Find Nashville and select it. (Note: It’s called Nashville-Davidson in the city file.) You can do this by

    going to SELECTION| SELECT BY ATTRIBUTES. Set up a query to look for

    CITY_NAME=’Nashville-Davidson.’ Once you find Nashville, get ready to label it. First, turn off the dams layer, so we can see the cities more clearly and zoom in to Tennessee.

Labeling Points

    To label points, first check what field ArcMap is using for the label for cities. Do this by right-clicking on CITY in the table of contents and choosing properties. Click on the LABELS tab. Make sure CITY_NAME is the field used as the label.

Next, on the drawing menu, find the labeling tool:

You’ll get another prompt from ArcMap asking how you want to

    label:

Choose the default options and click on Nashville.

You should be able to click on the city name with the regular

    arrow and move it a bit to where you want it. Your map should

    like something like this:

    We could edit the symbology to choose GRADUATED SYMBOL and we could make the pushpin different sizes based on the population.

Practice Exercises

    1. Colorcode the dams to show EAP (whether they have an emergency action plan) 2. Code dams to show different categories by age of the dam

Querying A New Map

    Now we won’t lose track of Nashville. Now let’s look for problem dams near the city.

    Begin by turning on the dam map. Things get a little cluttered, but it will get better.

    Let’s say we want to look for all the dams within 50 miles of Nashville. To do that, we’re going to create a buffer (or in this case, a circle) around Nashville.

    In ArcMap 9.x, some of the tools are hidden. You need to add them to your toolbar before you can use them. If you do not have BUFFER WIZARD under tools. Go to TOOLS | CUSTOMIZE. Click on the COMMANDS tab. Click on TOOLS in the left window. Drag the BUFFER WIZARD to the TOOLS menu. Close the CUSTOMIZE box.

Now, back to business. Go to TOOLS|BUFFER WIZARD.

    This wizard will ask you which layer you want to base your buffer on. If you only want a buffer around Nashville (instead of all cities) make sure to check the USE ONLY SELECTED FEATURES BOX. The click NEXT.

    The next box will ask you how big you want your buffer to be. Let’s say 50 miles. You also may have to make sure your buffer distance units are in MILES. Click next.

    The next window asks if you want to dissolve your circles together or keep them separate. In this case, it doesn’t matter because we have only one buffer. If we had several cities selected we probably would choose NO, as we would want to address each city separately. Here we’ll create a new layer with our

    buffer be sure to give it a name. Let’s call it nashdams.shp

    Click finish and you’ll see that ArcMap has added a circle around Nashville. To see the dams within the circle, double-click the buffer layer in the table of contents and change the symbology. Double-click the symbol. And choose HOLLOW as the type. This will allow us to see the buffer and the dams.

    Your map should look something like this:

Report this document

For any questions or suggestions please email
cust-service@docsford.com