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11. GIS Book: Frequently asked questions

Fundamentals of GIS ArcGIS 10 Manual PDF

Which zone do I select if my study area shares two UTM zones?

What you usually do in this case is work with the UTM zone that contains most of the study area.

If I copy an MXD project, will all the map layers (shapefiles and images) be copied?

No, an MXD file simply manages file paths and displays settings for legends, display scales, case selection, etc., among other things, but not the layers themselves. Before starting a project, it is recommended to store all layers within a single directory. In the File > Map Document Properties menu, select the Store relative pathnames to data sources check box to make it easier to connect files linked to the MXD.

You can also package a map project and all associated layers. To do this, go to the File > Share As menu to create a Map Package. The reader is allowed to investigate the uses (and drawbacks) of this tool.

How do I put labels on a layer?

Labels allow you to display the information of the elements that make up a layer: for example, if you want to display values for a layer of contour lines, hospital names in a point layer, the name of national parks in a polygon layer.

To add labels right click on a layer and select Properties. Go to the Labels tab and select the Label features in this layer check box. In the Text String section in Label Field select the field containing the information to be displayed on the map.

Although in the Label tab you can configure the style, positioning and other options for labels, for greater personalization you can change the tagging engine from the View > Data Frame Properties > General Tab > Label Engine > Maplex Label Engine menu.

What are the main elements that a map should have?

This depends on many factors, among others: the map’s audience, size of the paper to be printed, distance from which it will be visualized, etc. Assuming that we are preparing a map for an academic work or consultancy, from our point of view the elements that will always be necessary are the graphic/text scale, the legend (s), the grid of coordinates and the north. If the map is presented on a separate page, it is highly recommended to use boxes, where the title of the map, the authors, the institution where it was made and the date will be indicated; for example, if the map is part of a text document and is to be inserted in the same, the title of the map must be in the figure footer.

What is the difference between projection and datum?

In simple terms, projection is the method used to represent the curvature of the earth on a flat surface, and datum is the set of parameters that are used to do it.

Is it possible to create several layouts in ArcMap?

No, you can only create one per map project (one for each MXD).

Can I insert a grid of flat coordinates and a grid of geographical coordinates?

Yes, it can be done. In the Data Frame properties, go to the Grids tab > New Grid.  You can add multiple grid coordinates.

Why don’t my data have a reference system?

This problem is very common in GIS.  It is possible that the person who created the data did not define the spatial reference system used. Nor can one guess the reference system used if there is no record. In shapefiles the reference file has a PRJ extension.

Can I import CAD files into ArcGIS?

Yes. Let’s assume we have an AutoCAD (DWG) file that is storing a topographic map. Click on Add Data and locate the AutoCAD file. Double-click on it and a list of files, which are actually the types of geometries contained in the AutoCAD file, appears.  Now let’s assume that we want to export the contours from the AutoCAD file. The contours are always polylines, so choose Polyline and click on Add. With this we have uploaded all the polylines of the AutoCAD file into ArcMap. Since we only want to export the contours (we will assume that these are in layer 27), we have to tell ArcMap that we only want to visualize this layer. To do this, go to Layer Properties and click on the Drawing Layers tab; this deactivates all layers and activates only the layer of the contours. When only the contour lines are visible, we can export the layer to any vector format (Data > Export Data).

Can I add new symbols to ArcGIS?

Yes. New symbols can be inserted in the style manager. Go to the Customize > Style Manager menu. Go to the Windows local user style file. Choose a category and right click on New.

Is it possible to convert a slope map from degrees to percent?

Yes. It can be done with Raster Calculator. The formula is:

s[%]=tang(s[°])*100

where s[%] is the slope in percent and s[°] is the slope in degrees.

Can I import a shapefile table into Microsoft Excel?

Yes, at least in the old versions of Excel, and also in Excel 2016. You have to open the program and tell it that you want to open a file. In the file type, indicate dBase (*.dbf). With LibreOffice you can do it, too. But be careful – the fact that it can be done does not mean that it is advisable. In fact, it is not advisable, because if you do something unexpected, like delete a column or even delete a row, the shapefile may be damaged and become unusable. We recommend you to copy only the DBF file to another directory and then open it and modify it as you want.  Any modification of the database associated with a shapefile is recommended to be done in a GIS.

Can I convert a point shapefile to polygons?

It’s possible, but the outcome may not be what you expect. To put it simply: from, say, 100 points, and without violating the topologic rules, you can form a number of different polygons. On the other hand, there is a tool that generates a single polygon from a layer of points. It’s called Minimum Bounding Geometry and can be found in ArcToolbox, under Data Managemet Tools > Features. Its use is very intuitive. 

Why does ArcGIS usually close unexpectedly?

ArcGIS applications sometimes close unexpectedly for no reason. When you agree to submit the bug report, it is sent directly to the Esri developer team. Some bugs are usually corrected by installing the Service Pack for each version.

When I export a map to PDF, why not all the symbols are properly displayed?

Usually, when special characters are used when exporting a map in PDF format, not all characters are displayed. It is recommended to export in PDF format from File > Print using a local PDF printer.

How can I view the Table of Contents if I have closed it?

Sometimes we accidentally close the Table of Contents. We go crazy for a while because we think it’s a toolbar and try to activate it where toolbars are activated. However, to reactivate the table of contents, go to the Windows menu > Table of Contents.

Is it possible to calculate the centroid of a polygon?

Of course. This is very easily done with the Feature To Point tool in ArcToolbox > Data Management Tools > Features. The operation of this tool is very simple. Just remember one thing: if you activate the “Inside (optional)” checkbox, all the points will fall within their respective polygons, but these points will not always be the centroids of the polygons in the strict sense of the word centroid.

Why are the layers of my project displaced?

It is quite possible that the layers have different spatial reference systems. It is also likely that the scale of work and inputs were different at the time of generating the layers.

How can I know the resolution of a raster?

Click twice on the layer, go to the Source tab and in the Property table you search for the Cell Size (X, Y) row (in my version it is the third one). Be careful! Don’t get confused: in this field there are two data, the resolution in X and the resolution in Y. So if you see 3,3, it doesn’t mean that the spatial resolution of the layer is three point three meters, but rather that the resolution in X is three meters and the resolution in Y is three meters. GIS can theoretically handle raster layers of different resolutions in X and Y, although this layer type is very rare. To the best of the authors’ knowledge, only some GIS like GRASS or R can handle these situations properly.

Is the pixel size equal to the cell size?

Yes, the pixel size is the cell size or spatial resolution of a raster. According to (ESRI, 2016d) a cell must be small enough to capture the necessary detail and large enough to run analysis tasks and efficiently store the information. The smaller the pixel size, the higher the raster resolution and the file size.

How can I copy a shapefile to another computer?

You can easily use ArcCatalog. This program has similar features to Windows Explorer, but with GIS layers, so it is very easy to copy, cut and paste GIS layers, including shapefiles. If you want to do it with Windows Explorer and, for example, you want to copy the layer “road_network.shp“, make sure to copy all the files that are in that directory and whose names start with “road_network” because, as you know, a shapefile layer is composed of several files, at least three and in most cases six.

Can I open an MXD in a previous version of ArcMap?

Not in principle. What you can do is save the MXD as a project file from an earlier version of ArcMap. This can be done from File > Save A Copy and in Type you choose the version of ArcMap for which you want the project file to work. Remember that the higher versions open the project files of the lower ones, but not vice versa.

Do I have problems running an ArcToolbox tool?

If opening an ArcToolbox tool gives a message similar to this “Unable to execute the selected tool. You do not have the necessary license to execute the selected tool “, you must be sure that you have a license for the extension you want to use. To activate an extension, go to Customize > Extensions menu. Extensions are only activated if you have a license.

In some cases when you try to open an ArcToolbox tool, it sends the message “Do you want to open or save this file?” with reference to the MdDlgContent.htm file. To fix this error, Microsoft Windows Programs must be selected as the default in Windows settings.

Why can’t I select A1 in the print size?

The default paper size available in ArcMap depends on the printer options installed. If a printer only supports A4, it is not possible to select a larger size. To select any paper size in the print window (File > Print) uncheck the Use Print Paper Settings check box.

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