The basic concepts of desktop GIS software haven’t really changed very much since their inception with MapInfo Pro software some thirty years ago. The original designers of desktop mapping software wanted to use the new Windows operating system to emulate the functionality only previously available with the help of skilled cartographers.

The concept these early designers wanted was to emulate  paper map creation but in a digital format. One of the main ways they achieved this was by using a process whereby each element of the map could be built up through creating a series of layers prior to printing the final output. Features which we now take for granted such as zooming and panning where at that stage innovative and novel to new users of GIS software.

If we look at a screen shot from QGIS we can see that the map area is displaying a map of Mexico. On the Layers panel on the left side there are five separate layers shown. Each layer represents data in either a point, line or polygon format. All of these layers are in a vector data format.
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Vector data could be defined as a list of values. For example, a point has a pair of x and y co-ordinates, a line has two pairs of x and y co-ordinates and a polygon has points where the first and last co-ordinates are joined to create an enclosure.

The layers have been brought into QGIS as individual layers which means they will display in a random colour. If these layers had been brought in as a project file each layers’ defined colour scheme would have been preserved.
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The next thing to note is that although we have five layers only one layer is currently displaying. This is because top polygon MEXICO layer is hiding the features of the other layers. Again, if this had been loaded as a project file the correct layer order would have been preserved.
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Clicking on the MEXICO layer and moving it as shown in the next screen shot will reveal the other layers’ details.

Now we can see that some layers are still not displaying correctly because they are being hidden by layer MXCTY_2K. Two options are now available. Firstly, we could turn off this layer as shown in the next screen shot.   

With this layer hidden, by clicking in the box next to the layer name, we can see the other layers more clearly making the map more informative. Alternatively, we could move the MXCTY_2K layer down to just above the MEXICO layer which will allow the layers above to display correctly.
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Attached to each layer is an attribute table. An attribute table is very similar in appearance to the spreadsheet format. The attribute table for the MXCTY_2K is shown in the following screen shot.

This attribute table contains 2128 records. Each record has two fields: City and State_Name. The attribute table has many useful features and can be used with many different aspects of the layer.
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As well as the attribute table the layer also has a Layer dialogue box option as shown in the next screen shot. Here we can label the layer and carry out many other actions to enhance our map.

We can also change the symbol colour and size to make this layer stand out more clearly as shown in the next screen shot.

As the map is very busy with so many labels we could set the layer visibility so than the labels only show at a certain zoom level as shown in the next screen shot.

If we zoom into the map to a level at which you want labels to display for this layer, we can do this as shown in the next screen shot. Once we have set the layer display if we zoom out the labels will no longer display.

As you can see we have made a number of changes to this project in order to make the layer display as desired. Many more changes would probably be needed before these layers are acceptable.

In summary, we have seen why layer order is important to ensure that all the map layers display correctly. Each individual layer possesses properties which can be modified to make the final map display successfully. You can set layers to display their labels at certain zoom levels so as to ensure that the output is legible and not overcrowded.
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Finally, each layer has an attribute table which looks similar to a spreadsheet. The attribute table can be used to interrogate the map and can be used to label the map with a specific field. In the above case we used the City field of the MXCTY_2K layer to display labels only at a specific zoom level.

If you are new to using GIS software or a casual user you may be surprised to learn that standard formats such as shape files do not contain sufficient information for successfully transferring data between systems.

For instance if you have been sent some shape files together with how they should appear in your system, and you are presented with something different when they are loaded, there is a simple explanation.

Here is a screen shot of how two layers should display in your system.

And here is how it may look if loaded in just a default shape format.

The problem is that shape files layers load into most GIS software packages with a random colour. If you load the same layer a number of times it will load each time with a different colour. Also shape files do not contain any information about how the layer should display or whether labels should be in a specific font, colour etc.

The shape file is a format developed by Esri for their original ArcGIS software system. This format is now a standard within the GIS community. However, whilst the shape file contains valuable information about how the layer should display together with any associated attribute data, other information such as layer styles and labelling information are not included.

GIS software packages have methods of dealing with saving and successfully restoring layer styles and labelling information by using project files. Then when the layers are reloaded, by using this project file method, all the appropriate information is automatically restored.  This may also include layer order and thematic layer information.

One of the main problems with the transfer of all the relevant information between different GIS software packages is that the project file format is not compatible between systems. For example, MapInfo Pro has a wor. format project system to save layer information together with other important data. All the other major systems such as ArcGIS Pro and QGIS also have similar project functionality

There are a number of ways to address these compatibility issues. Firstly, the layer information can be saved in a separate layer file which has a .lyr format. Then each layer can have its own layer format file so as to ensure the layers display correctly. There are now a number of such layer formats available. Unfortunately, not all of them are compatible but it should be possible to find one which will work between the GIS software packages that you use.

The Microsoft windows file management system was developed to enable users to easily save, copy, delete and move files within a hierarchical folder structure. Each file type is identified by a dot definition system. So a Paint program file could have a .png, bmp or .gif format. A text file could have a. .doc format.  An excel spreadsheet could have a ,xls format. This file management system works very well for file types which generally consist of a single file format, however GIS formats such as Esri shape files or MapInfo tab files are made up of a number of different file types. This often presents a problem for casual GIS users when copying, deleting, moving or saving such files through a file management system such as Microsoft Windows. Often only the .tab or shp file element is copied which means that the specified file will not load into a GIS system.

In the above screen shot from the Windows file management system the shape file format can be seen to consist of four files, all of which are needed to produce a map layer in a GIS.

ESRI have addressed this problem with the introduction of ArcCatalog, which is there own proprietary file management system. Within ArcCatalog various filetypes are stored is such a way as to enable the user to access the various elements as if they were a single file. Additional features enable users to preview maps within ArcCatalog as well as the ability to drag and drop files into the map surface.

MapInfo and QGIS have developed similar interfaces to ArcCatalog to enable users to correctly copy, move, delete and save shape and tab files.
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Here is a screenshot of the MapInfo Map Manager application.

Here is a screen shot of the QGIS browser.

These GIS file management systems have features not available in the standard Windows file management system. For instance the QGIS browser has tabs which allow users to view a variety of different aspects of the data including metadata, attribute data and map views. Files in the browser can be dragged and dropped in the QGIS map frame as an alternative to opening the file via the standard GIS file menu system.

The shape and tab file formats have been around since the beginning of desktop mapping. MapInfo introduced the first desktop system in 1986 which gives you an indication of how long these formats have existed.

As they are still used and therefore relevant, it is always useful, for even the most casual user of GIS, to be aware of the file structure of shape and tab files as they are still going to around for the foreseeable future.

You can use attribute data attached to individual layers to find out about information relating to projects within your GIS. Additionally, you can also find answers to questions regarding  the spatial relationships of the features within a selection from within the layers.

This ability to query spatial relationships enables you to answer questions such as, how many airports are within a region, which rivers cross boundaries, which countries have a common border or how many cities have a population in excess of two million within a specific country.

In the same way GIS can also answer questions about health, income, crime levels and employment within a certain geography.

Looking at the London boroughs we could ascertain, with the help of GIS, which are the poorest and which are the most affluent.

Here is a map of the London wards. There are 4765 ward entries in the attribute table for this map layer.

If we just wanted to query data at a borough, rather than the ward level, we could use GIS to create a new layer. We could achieve this by using a geoprocessing tool to dissolve the current 4,765 wards into 33 boroughs. This results in a map layer similar to the following screen shot.

If we also download spreadsheets containing information about health, education, income and employment they could be joined to our London borough map attribute table to give us a picture of each boroughs’ performance.  .

Here is a map showing crime levels across the 33 London boroughs. The darker the colour the higher the crime levels.

The next map shows employment prospects across London.   

Employment is greatest in the lighter areas. The darker the colour the less likely for employment prospects.

The next map shows health prospects across the London boroughs.

Here the darker the colour the better your health prospects are.

The next map looks at income levels across London. Here the darker the colour the higher the income levels for that borough.

The next map examines educational levels achieved across the London boroughs.

The darker the colour the lower is the educational achievement.

Looking at these maps should give an indication of which areas of London are most affluent and which are the poorest. However, we can use GIS to confirm which are the most affluent or which are the poorest across the criteria of crime, employment, health, education and income.

​And here is the result of using an SQL statement within a GIS to find the London boroughs with the best average scores on crime, employment, health, education and income levels.

Out of the 33 London boroughs only three met the criteria and are highlighted on the map above.

Each feature within a GIS has appropriate attribute data attached to it. This data can contain information such as, in the case of a city, its name, size of population and other relevant details.
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All GIS store data in a format which is commonly referred to as an attribute table. Each layer contains an attribute table which is similar to a spreadsheet layout. Within this table the user can put as much or as little information as is required for the layer’s requirements. Like a spreadsheet the data is stored in a series of rows and columns. Each row represents a single record and each column represents a field within the table. Some tables only contain a few fields with a limited number of columns, whilst other tables, say containing crime statistics, can have thousands of records and numerous fields.

Information within the attribute table is linked to the point, line or polygon within the map layer. Clicking on one or more features in the map layer will also highlight the same features in the attribute table if this has been made visible. Similarly, clicking on one or more rows in the attribute table will highlight these features in the map layer.  

The fact that the map layer and the attribute table are linked enables us to be able to ask questions about the data contained within the table and show the results on the map layer. We could query our data to find, for example, the largest cities or the number of airports within a region or where the population is over a certain level. In fact, the modern GIS enables us to ask an almost unlimited number of questions about the data contained within the layers of the map.

As well as being able to highlight features on our map layer we also have the ability to create thematic maps based on the data within the attribute table. Sometimes, it is easier to understand the underlying data within the layer when we create a thematic representation of that information. For instance, population by region can be easily be shown by using a thematic representation.

As well as being able to ask questions about data within a single layer it also possible to create a query which covers multiple layers. To do this we can use the SQL feature, which stands for standard query language, available within the GIS.

Some GIS software such as MapInfo Pro and ArcGIS Pro have always had features to enable users to create quite sophisticated queries from layers within their proprietary software. Until recently, QGIS, which is open source, was not able to match this level of sophistication. Now however QGIS has a feature which can enable users to create sophisticated queries using the virtual layer facility.

Desktop GIS now has many features which enable the most complex questions to be asked about the layers within a project. The visual results of such queries can often give a greater insight than the equivalent spreadsheet bar or pie chart can achieve.   

 Desktop geographical information systems use scale to represent the relationship between the size of elements within the map and the related areas within the real world. In fact it is very similar to the methods used with paper maps. However, paper maps are produced at fixed scales to meet different requirements. This contrasts with the flexibility of a desktop GIS which can produce an infinite variety of maps by adjusting the scale to meet specific requirements.

A ramblers paper map would have a scale which relates more closely to a specific area of interest. A map used for travelling over larger distances by car for example would have a different scale. The only way someone could take a closer look at a detailed paper map would be to use a magnifying glass which would have no impact on the scale of the map. However, with a desktop GIS  there is the capability of zooming into areas of interest which then  automatically adjusts the map scale.

So with a desktop GIS the zoom feature enables users to view maps at a variety of scales. In the following screen shot the map is shown at a world view of 1:186,760,885.  

In the next screen shot the scale has been changed to 1:13,877,198 as we zoom in to take a closer look at an area including parts of the United States and South America.   

The effect of zooming in shows that in the above map is now nearly fourteen million times smaller than actual size. The map now has a scale value of 1:13,877,198. The zoomed in area of the map within the GIS has in other words a ratio 1:13,877,198. This represents one unit on the map as almost fourteen million times smaller than in the real world.

We can also indicate the scale of a map by adding a scale bar to maps that are printed. We can set the scale to the desired measurement which could be either metric or imperial. In the following screen shot we have set the scale in kilometers.

So as we zoom into a map we can obtain a closer view of the map’s features. At different scales we can obtain just the right amount of information for our specific requirements. The ability to create a variety of maps from a single map source is made possible by the flexible scaling features within a modern GIS system. Maps can then be printed at a suitable scale to meet the user’s requirements.

Prior to the availability of computerised mapping facilities paper maps were often used in conjunction with acetate sheets in all forms of mapping applications. At that time the latest paper map of a county or region would have been an expensive outlay. Within the UK, local authorities obtained their paper maps from Ordnance Survey often buying updates several times a year at a cost of thousands of pounds.   

Because the maps were expensive it made sense to ensure that they were well looked after. Sometimes this was achieved by laminating the maps to stop them being damaged by accidental spillages. If additional information was needed to be added to these base printed maps, acetate sheets were used. These acetates were used to mark out, for example, property boundaries or crime incidents. In this way several layers of information could be added without causing any damage to the printed base map.

Today, the modern desktop gis uses the same principal to separate the base map from other information stored within the system. The layer system enables the user to break information down into specific areas of interest. For instance in a map of Alaska all the airports are contained within a separate layer within the gis. This information on its own would not make a great deal of sense without the underlying base map as the following graphic shows.

Without the underlying Alaskan base map the airport layer does not make a great deal of sense as it is not related to anything meaningful in isolation. In the next graphic the airport layer makes sense as it shown with the relevant base map.

Maps can have many layers within a project. Layers can be present within the map without being visible. This enables specific areas in the project to be analysed by the map maker. Often a map may contain very many layers and it this case it makes sense to group related layers. In grouping layers you can then more easily manage whether the group is displayed or not. The group of layers can then be turned on or off together rather than manually turning off the related individual layers one at a time.

Some gis systems, such as MapInfo allow placement of points, lines and polygons within the same layer. However, whilst this is possible within MapInfo, if you need to transfer to a different gis you may find this creates problems. Both QGIS and ArcGIS have a layering system which only allows for one type (point, line or polygon) to display within a layer. Transferring data to QGIS from MapInfo with layers containing a mix of types will result in QGIS creating additional layers during the conversion process. Alternatively, MapInfo can convert layers to a shape file format which both QGIS and ArcGIS can then use.

Layers can be in a vector or raster format. Vector layers are either points, lines or polygons which can be in an x and y, or latitude and longitude format. Raster data consists of a series of dots and is often used to represent for example, ocean depths or variations in vegetation growth. In the next screen shot a raster layer has been added to the Alaskan map.

Layer order is important when displaying data within the map. If the layers are not ordered correctly some layers may not display correctly, if at all. To change the layer order you only need to click on the layer within the layer control section, hold the mouse down and then move the layer up or down to achieve the correct sequence.

Maps have been used for a long time as a means of providing a visual understanding of the world around us. Some famous examples of maps have had a dramatic effect on our environment and our perception of the why events occur. 

The map of the 1854 Broad Street cholera outbreak clearly shows how the epidemic spread from residents drinking contaminated water. John Snow’s study showed how the contaminated water supply was linked to the maximum fatalities in close proximity to a specific water pump. These fatalities were represented by points on the map. The most points surrounded the contaminated water supply. Thus a map was able to prove what John Snow suspected as the cause of the outbreak.

Another famous map shows in graphic detail how Napolean’s army was decimated during the 1812 Russian campaign. This map is basically a graph or flow chart of the size of Napolean’s army on entering Russia and how it was reduced to a ragged remnant towards the end of the journey back.

Both these maps were the work of skilled cartographers. They would probably have been amazed at the way in which modern GIS systems can produce diverse maps without the cartographic skills they had spent years developing.   

With a modern desktop GIS a map of Alaska could, for instance, show a variety of different scenarios from the same base map. Below is an example of a base map of Alaska. 

Since the advent of desktop GIS mapping solutions it has been possible for virtually any individual or organisation to produce maps to meet their specific requirements. Mapping is no longer the specialist area of skilled cartographers producing maps by hand. Nor is mapping the domain of large corporations who, in the not so distance past, could afford the mainframe and mini computers which cost millions to buy and maintain.

All modern gis systems can produce such maps without the user having to need any specialist cartographic knowledge. Although a general understanding of cartographic principles would obviously be useful in order to produce quality output.

The map below of Alaska contains a number of layers showing the regions, airports, lakes and many other features of interest.
In most cases the final map, for printed output, will contain a legend to explain what the various points, lines and polygons represent.  

If you have used previous versions of QGIS you may have noticed that most of the icons on the abc labelling feature were greyed out. In these earlier versions a number of steps had to be taken to enable a layer to access abc labelling features such as move, rotate and hide. For instance, fields had to be added to the layer’s attribute table for x and y coordinates for the move feature to work. Similarly a rotate field was needed for the rotation functionality. To hide labels required yet another field. Again these fields also had to be in the correct format. . Having created these fields correctly there were several more steps required to make the labelling function work. Each field had to be connected to the labels property function and then finally, if editing was enabled, the various features of the abc labelling application would become activated. Because of the amount of work involved, in getting these features to work for each individual layer, this functionality was mainly used by geographers who needed to place, move, rotate and hide layers where the standard features were insufficient. If you have previously used software such as MapInfo Pro you would have been surprised that manipulating labels required so many additional options. In MapInfo you can click on a label and move or rotate it without any of the previous steps mentioned. Once a label is moved in this way in MapInfo it is referred to as being personalised.    

With the advent of QGIS 3 the labelling functionality, which was previously only within proprietary software, is now available to open source geographers.   

Here, I have opened a project in QGIS 3 containing layers from the Alaska data set which is available for download with the latest versions of QGIS. As you can see I have moved the Label Toolbar to the map section on this occasion for clarity purposes. Normally it would be positioned on the top menu.

In this screen shot of the Label Toolbar only one of the icons is currently enabled. In earlier versions of QGIS, as previously discussed, most of these icons would stay greyed out without a lot of extra work being involved. However, if we now click on the regions layer in the Layers panel all of the icons will be enabled as shown in the next screen shot.

Clicking on the abc icon brings up the Layer Styling dialogue panel. As we have selected a layer with labelling enabled we have a number of options available.   

If we switch to another layer such as airports we no longer have any features enabled as shown in the next screen shot. You can do this either by selecting airports from the drop down section of Layer Styling dialogue panel or by switching from the regions to the airports layer in the Layers panel.

To create labels on a layer first you need to select the Show labels for this layer option from the drop down list as shown in the next screen shot. Then select an attribute from the layer’s attribute table to label the map with.

 On the Label Toolbar there are six buttons for modifying labels. Starting from the left is the Highlight Pinned Labels function which will show those labels which have been modified in some way. The cursor appears as a cross on the map when the Label Toolbar is activated.

Similarly the Pin/Unpin Labels function will enable labels to be modified as well as reverted to their previous state.

If you want to hide a label first click on the Show/Hide Labels function as shown in the next screen shot.  

 Placing the cursor over a label as in the next screen shot. The cursor is represented by a cross.

 Pressing the Shift key together with a mouse click will hide the label as shown in the next screen shot.

To hide several layers follow the above process but create a rectangle around the labels you wish to hide. Similarly, to show labels either click or create a rectangle around the area where the labels are hidden.

The Move Label and Diagram icon enables labels to be moved as necessary. In the next screen shot I have clicked on the Northwest Arctic label and moved it to the left.  

 Once in the desired position letting go of the mouse button will place the label in the new position.

Enabling the Rotate Label and clicking and holding down the mouse whilst rotating as desired will reposition the label.

​ Here we have clicked on label and rotated it 24 degrees.

 Once the mouse is released the label will stay in its new position as shown in the next screen shot.

The Change label option allows you to modify the look of individual labels. Click on a label and the Label Properties dialogue box for the label will appear as shown in the next screen shot.

 As you can see there are numerous options for personalising specific labels with this dialogue box. This option enables a label to have a variety of changes simultaneously rather than using the individual options to move, rotate or hide.

As mentioned earlier the improvements to the labelling functions in QGIS 3 makes modifying labels a much easier task than with earlier versions of QGIS.

Geographic joins

Intersects: this geographic function compares data within two tables.

A point, line or polygon intersects another point, line or polygon when they have at least a node in common: a network crosses another network for example a road or a railway line.

The intersection means a geographical geometry touches or goes through another.

Contains and its reciprocal Within means geographical geometries are within another geometry.

A geometry A contains a geometry B when it contains the centroid of B.

When B is within A: for example a catchment area contains clients represented by point geometries.

Entirely within and its reciprocal Contains entire.

A geometry A is entirely within a geometry B when the group of nodes of A are within B.

According to the type of the compared geometry, according to needs, depends on which of these operators are chosen.

Generally, use the Intersects function to compare polygons or from polygons to lines. ​
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The dialogue box in the Info section states that Project layers: Not connected.

In the Providers section double click on the Project layers option.

The various layers are now displayed

Click on the Ilots_Saumur option and view the Info, Table and Preview tabs​

​In the Tables drop down list choose the Ilots_Saumur and Buffer_Stop_Points tables

Click in the Columns section and from the Columns drop down list choose

Ilots_Saumur.PSDC99

Buffer_Stop_Points.ID_PA

Ilots_Saumur.geometry​

Buffer_Stop_Points.geometry

Choose Ilots_Saumur.geometry from the Columns section ​

Put a comma after this entry

Then choose Buffer_Stop_Points.geometry and add a closing bracket​

Click in the Group by section and choose Buffer_Stop_Points.ID_PA from the Columns drop down list as in the following screen shot

Click on the OK button​

Click on the Execute button or Ctrl + R

Select Load as new layer by ticking in the box

The Co-ordinate Reference System dialogue box appears. Click OK to accept the default co-ordinate system​

Name the layer as “Population data where buffer intersects” in the Layer Name section​

The layer is loaded into QGIS

If you wanted the find the population data for the areas which intersect the seven buffers we could modify the SQL as follows

This will create a new layer similar to the previous one but with a different attribute table as shown below.

With virtual layers you can create more complex SQL statements than is possible with the QGIS field calculator.  Now it is possible to use ESRI shape and MapInfo mif files to create SQL statements previously only feasible with  PostGIS, MySQL and Oracle Spatial formats.