We want to display some other themes as well. Go ahead and click on the small box to the left of the theme name "Iganga-roads_50000.shp" in the Table of Contents so that a check mark appears in the box. We can now see a small square in the Iganga area on the map drawn on top of the map of Uganda districts.
(Note: theme names with "50000" in them were purchased from the National Biomass Project in the Department of Forestry, Kampala, Uganda. The Department of Forestry sells these square-shaped data sets that cover an area approximately 27.75km by 27.75 km with a resolution of 1:50,000. Thus the theme appears as square shaped in our View.)
Now check the box next to the theme "Iganga-urban_50000.shp" in the Table of Contents.
Notice that you can hardly see this addition to our map. This theme actually appears as a very small set of polygons representing settled areas, especially the town of Iganga. This indicates that in GIS we can have themes at different spatial scales (area of coverage) all tied to the same spatial database. How do we get to see a closer view of the themes of "Iganga-roads_50000.shp" and "Iganga-urban_50000.shp" on our map?There are several tools that enable us to navigate through different spatial scales.
We need to examine several buttons at the top of the screen to illustrate how we can navigate in ArcView.
We want to zoom in to the small Iganga area covered by our two Iganga themes displayed in our map.
In the second row of buttons located at the top of the screen below the menu, click on the zoom-in button
and drag your cursor on the map to create a rectangle around the small Iganga area. Release the mouse button when you have outlined the area that you want to examine. The small area that you outlined with your cursor will now expand to fill the entire map in the View.
We can now see the roads and settled areas in the Iganga themes (which includes a part of Jinja District). We can also see the outline of the Uganda district boundaries below the two Iganga themes.
Similarly, you can zoom back out in the map by clicking on the zoom-out button
at the top of the screen and then clicking your cursor in the center of the map. After you click on the map, the map will be redrawn to show a larger area. You can keep on clicking to show progressively larger areas.
After clicking on your map twice, your View should look something like this.
These two zoom tools will zoom in and out at 2X by holding them over the center of where you wish to zoom in and out and by making a single click with your cursor.
You can also move the map in any direction without changing the scale of the view. Click on the pan tool button
located at the top of the screen below the menu and then place your cursor--which should now look like a hand--on the map. Drag your map with your cursor in any direction and you will move the map in that direction as well and see areas previously hidden from view.
We can also zoom in on the full extent of an active theme.
We make a theme "active" by clicking once on its name in the Table of Contents so that a raised rectangle appears around the theme name. For example, make the theme "Iganga_topog.shp" (which displays lines of elevation) active and click on the box next to the theme name so that a check mark appears in the box. We can now see the lines of elevation in part of the theme in our View, but not all of the theme.
To change the scale of the View so that an "active" theme fills the entire View, go to the buttons at the top of the screen below the menu and click on the Zoom To Active Theme(s) button:
We now see that the theme "Iganga_topog.shp" fills the entire View.
We can also shift back to our original perspective when we saw the map of all of Uganda.
We know that our map of all of Uganda is represented by the theme "Uganda_district.shp", which has the widest spatial range of all the themes, so we want a tool that will let us zoom back to the widest extent possible.Go to the top of the screen to the top row of buttons below the menu. Click on the Zoom to Full Extent button.
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This button tells ArcView to zoom out to the farthest extent possible to the outer boundaries of the theme in the Table of Contents that covers the biggest area.
We now see all of Uganda. Your map should look like this in relation to its areal extent.
Two other buttons are important.
The Zoom to Selected button
redraws the map out to the farthest extent of features that have been selected (if selected, they will appear in yellow, as will be explained in another Step).
The Zoom to Previous Extent button
allows you to zoom back to the previous View. You can change back to the previous View up to four times by clicking on this button.