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.

Joining an Access table to a table in a personal geodatabase within ArcGIS software is currently only feasible with ArcMap. However, as discussed in a previous blog, you could import your Access database tables into a format which is acceptable to ArcGIS Pro. In this case creating a join to Access tables in ArcGIS Pro would be possible.

Prior to discussing how to join Access tables in ArcGIS Pro it is relevant to quickly review the history of personal geodatabases and a possible reason for ArcGIS Pro currently not supporting Access tables.

Personal geodatabases were introduced with version 8 of ArcMap. Personal geodatabases use the Microsoft Access .mdb format and are only available on the Windows operating system. A personal geodatabase has on average an effective size of up to 500 mb. Whilst the maximum size of Access tables is theoretically 2GB in reality because of performance issues 500 mb is recommended as the optimum size. Additionally, Esri has also now developed the file geodatabase which gives better scalability, performance as well as cross platform use.  

Since ESRI introduced ArcGIS Pro, Access database connection availability has been limited to ArcMap. Some users may choose to use ArcMap for Access connection and ArcGIS Pro for other work. ArcGIS Pro has many attractive features, which take advantage of the new Windows 10 ribbon interface, which are superior to the menu based system used by ArcMap.

ArcGIS Pro may not support Access database connection because of problems experienced with connecting Access databases to ArcMap. This could be because personal geodatabases and older Access tables share the same .mdb format. As the personal geodatabases use .mdb files they could be accidentally corrupted by users modifying these tables within the Access software.

As mentioned in the previous blog you can easily import Access databases into SQL Server and then access these tables in ArcGIS Pro.

Here is a screen shot of the Observatory database, which has been imported from Access, into SQL Server Management Studio. Here we can see the table which we can use within an ArcGIS project.

If you are using ArcMap and regularly need connection to Access databases you should be aware that if you decide to upgrade to ArcGIS Pro there is currently no Access database connection facility.

There have been some suggestions that since ESRI introduced a ribbon based interface, issues with Windows 10 are the reason for not having an Access connection. However, MapInfo Pro is now also using the same new ribbon based interface with Windows 10 and has no problems with connecting to Access databases.
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Microsoft Access 2007 introduced the new  .accdb file extensions which replaced the .mdb file extension.  Currently ArcGIS Pro does not connect to the .accdb format.  However,  ArcMap can connect to this newer Access format.

You can work with Access tables of an .mdb format in ArcMap via an OLE DB connection. OLE DB is the standard for sharing data between applications. This enables connection to Access databases in ArcMap. However to ensure data is not corrupted changes should only be made within Access and not via ArcMap.  

For the same reason, modifying a personal geodatabase should only take place within ArcMap. Modifying these files, which are in an Access .mdb format, within Access could lead to the geodatabase file being corrupted.

Access is not recommended for editing personal geodatabases as it was not created for use with the ArcMap geodatabase format. In addition, unlike many other relational databases Access does not support geometry. The ArcMap geodatabase has to keep track of the table changes whenever a user update occurs. For this reason modifying these tables in Access could corrupt the geodatabase.

As there have been problems with Access connections to ArcMap geodatabase files, there is some logicality in ESRI currently not providing an Access database connection in ArcGIS Pro.

This obviously creates a dilemma for current ArcMap users who want to upgrade to ArcGIS Pro but also need to continue to connect to Access databases. One solution would be to use ArcMap for Access connection and use ArcGIS Pro where Access is not required. Running two different versions of gis software could lead to compatibility issues so this is not an ideal solution. The other problem is that ArcMap will not be supported forever and there will come a point where a decision to switch to ArcGIS Pro will become inevitable to avoid working with unsupported software. Currently, there is no information as to whether ESRI will provide Access database connection in ArcGIS Pro.

An interim solution could be to convert Access databases to another database format that ArcGIS Pro does support. Access is a Microsoft product and therefore the obvious route would be to use a Microsoft conversion tool for moving Access tables to another relational database such as SQL Server 17 Express.  

According to Microsoft the maximum size of an Access database is 2GB whilst the max size of SQL Server 17 Express is 10GB. So any current Access database should be well within the limits of the SQL Server 17 Express database.

SQL Server 2017 Express is a free edition of SQL Server, ideal for development and production for desktop, web, and small server applications. You can download the Express version here.  ​You should also download SQL Server Management Studio (SSMS) which you can use to query, design, and manage your databases, either on your local computer, or in the cloud.

Most importantly SSMS is also free! You can download it here.

Start up SQL Express and then SSMS. A dialogue box for connecting to SQL Express will appear as shown in the following screen shot.

Accept the default settings and you will be connected to the server as shown in the next screen shot.

The next step is to create a database for your Access tables. Right click in the Object Explorer pane on the Database folder. Select and click on the New Database option. 

Click on the Next button and choose the Access database connection option and browse to your Access database location as shown in the next screen shot.

Select Destination, Server Name and the Observatory database as shown in the next screen shot.

Click on the Next button and accept the default as in the next screen shot.

Next select the table or tables you wish to import as shown in the next screen shot.

Click on Next to show the next dialogue box as shown in the next screen shot.

The final dialogue box confirms the actions requested and imports the data into the SQL Server database as shown on the next screen shot.

Here is a screen shot of the Observatory tables within SQL Server Management Studio.

The Access tables are now available within SQL Server Management Studio. Now we can connect the imported Access tables to ArcGIS Pro.

Create a new project in ArcGIS Pro called Observatory and click on the Add New Item icon in the Favorites section in the Insert tab. Next choose the New Database Connection option as shown in the next screen shot.

If you are familiar with the Atlas feature in QGIS you will be pleased with the new Report feature available in QGIS 3, which is the latest version. With this new Report feature, as well as attribute driven pages, you can also add headers, footers and static pages to your pdf report. In this way your report will become more readable and meaningful to those you send it to.   

For instance, with the Atlas function you can iterate through a series of polygons, lines or points to create a map series based upon an attribute field of a specified layer. However, with the Report function, in addition to headers and footers, you can also have nested map series as well as static pages in your final report. Because you can generate a much more complex report with many sub sections, the benefits of headers and footers and their inclusion within the report, to make it meaningful, becomes more apparent.

When you include a nested map series your report will iterate through the attributes and group them based on a linked attribute in the top group layer. If your nested layer does not have an attribute field that can be linked you can create a link with the “Join by location” algorithm from the Tool Box.  

For example, if you wanted to link a towns table to a regions table you would use the algorithm to group the towns which are within in regional polygon to create a new table which can then be linked to the top group layer.

If you start a new project in QGIS 3 you can create a new report quite easily. Below I have created a new project with three layers. A French town’s point layer, a polygon regions layer and a graduated polygon regions layer.

To create a report click on Project on the top menu and select New Report as in the following graphic.

Next complete the Create report Title dialogue box and click OK.

This brings up the Reports dialogue box.

Here you can create both a header and footer for your report. When both header and footer are enabled you can click on the Edit buttons to create the relevant pages for your report. Below is a sample header page containing two text boxes.   

If you want to have a static layout page click on the green plus button. Choose the Static layout section option as in the following screen shot.

When you click on the Edit button a blank static layout page is created as shown below.

You can include text, images or legends in this section as shown in the following screen shot.

By clicking at the top level on the Report heading and the creating a Field group section we can then edit the Body section. We can create maps related to regional population by including attribute driven text fields together with a map zoomed in to region level and a legend. An example is shown in the next screen shot.

We can now add a nested section by leaving the Group section highlighted rather than going back to the top Report level. This nested section has a header page which is shown below.

Having created a header page related to each set of regional towns we can now create individual maps of each town within a region. You can see from the following screen shot that the map is using an OpenStreet map layer. As this report has both graduated symbol layers and OpenStreet layers ensure that Lock Layers and Lock Styles are enabled within the Items Properties section for each Field group section as shown in the next screen shot.

Also note that within each Field group section the maps are controlled by the report so you need to ensure that this option is also enabled.   

By clicking on the Report option on the top menu you can create a pdf for your report as shown in the next screen shot.

Depending on how many pages are included in your report and whether OpenStreet data is included will determine how long the report takes to be created. Below are some screen shots from the pdf generated by the above report.

Here is the static page screen shot.

Next the report will generate a map for each region of the French map as shown in the next screen shot.

Next the nested header page is printed as in the next screen shot.

Next the report will produce maps of the individual towns within the Alsace region as shown in the next screen shot.  

Note that the nested Prefecture sections show an OpenStreet layer whilst the Regional sections show a graduated symbol layer.  

This final screen shot shows the final page of the report.

As the above example shows the new Report feature has potential to produce both simple and complex reports which can contain a range of map formats. Because of its flexibility it represents a considerable improvement over the previous Atlas program.

​We could enhance this map by adding a mask as in the next example.

Some improvements to the program would include including an ability to recognise when the user closes one set of maps and opens new ones. This would also include closing any elements in memory which could impact adversely on the next set of maps. Also the cartographic element is very rudimentary.

The program currently is hard coded and only works with base maps. If a style override is applied this is not included in the maps generated by the program. The ability to be able to read this kind of data regarding layer information and apply it to the map series would be very useful.

You can obtain the Atlas program and the related MapInfo Pro tab files from the Pitney Bowes community download page with this link
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