27/12/2012

* Talk: GIS & Utility Mapping Seminar, Subang Jaya, 27.12.2012



Seminar GIS &amp Pemetaan Utiliti, Subang Jaya, 27.12.2012

Hari Jumaat, pada saat akhir, atas sebab-sebab yang tidak dapat dielakkan, Majlis Perbandaran Subang Jaya menjemput saya membentang kertas kerja mengenai GIS pada seminar tersebut diatas. Hari ini, seramai 60+ peserta menyertainya termasuk perunding perancang bandar dan wakil dari agensi-agensi sektor awam. Saya diberi peluang membentang kertas pertama dan memandangkan lain-lain kertas memperincikan aspek pemetaan utiliti, kertas saya menumpu perhatian kepada 'Understand GIS' yang saya menggangap sesuai sebagai pengenalan dan menjangka akan terdapat juga peserta-peserta yang tidak mahir dalam GIS. Pada penghujung kertas, diperkenalkan QGIS serta perbandingan dengan perisian berbayar dimana saya menyerahkan penilaian yang mana lebih baik kepada peserta. Saya harap penyampaian kertas saya ni OK.

GIS & Utility Mapping Seminar, Subang Jaya, 27.12.2012

Last Friday, a last minute plan saw the Subang Jaya Local Authority making a call and requesting me to present a GIS paper at the above seminar because due to unforseen circumstances, another party could not make it. Today, 60+participants attended consisting of planning consultants and representatives from public agencies. I was privileged to present the first paper and because other papers were heavy touching on utility mapping, I decided to present a light paper entitled 'Understand GIS' which I thought would be a good as I anticipated there would also be participants with basic comprehension of GIS. Towards the end, I introduced QGIS and gave a brief comparison between it dan proprietary GIS leaving participants to make their own judgement which is the better. I hope I presented well.

20/12/2012

Reprojection issues


Reprojection issues

Someone asked me to show him the effects of reprojecting a cadaster map using QGIS from Cassini-Soldner to fit over a Google Map because he was unsure of certain things. Firstly, I explained that in QGIS, 'reprojection' is fundamentally a 2-step 'save as' move. After showing him how to do it, he agreed the QGIS way is comparatively easier than the proprietary GIS he uses. Secondly, I said to reproject a map to a Google Map, there are 2 options where many prefer Geographic Reference System e.g. WGS84 but I prefer Projected Reference System e.g. Goggle Mercator. Why? I am not clever in this field to technically justify a counter-argument like 'So what? I still can do it using WGS84. What's the big deal?' Well, my humble explanation is shown using the QGIS Coordinate Reference System selector: Note WGS 84 (I don't mean the WGS 84/Mercator-kind version) falls under the earth-preference Geographic Coordinate System whereas Cassini and Google Mercator fall under the paper-preference Projected Coordinate System (remember, the Geographic and Projected CS are fundamentally different in approach). As such, I suspect reprojection from Cassini to Google Mercator would be more accurate and reprojection from Cassini to a variation of WGS84 under the Projected Coordinate System ought to produce results but how much different I do not know:

Cassini map on-the-fly projection
When put off-the-fly projection, Cassini map disappears
Cassini map projection puts it west of Africa in the context of Google Map projection 
Cassini reprojected WGS84 map puts it in Peter Pan's Neverland
Cassini reprojected Google Mercator map Round 1 puts it above West Malaysia
Same map re-zoom to layer extent Round 2 brings it down to earth
Same map rezoom to layer extent Round 3 greatly improves map alignment
Memandangkan reprojection peta kadaster ke Google Maps boleh dicapai selepas beberapa cubaan, saya menganggap CPU, RAM dan juga kad grafik memberi kesan akan paparan peta ke Google Maps tetapi tidak pasti sama ada faiz fail yang besar ada hubungkait terus mengapa isu paparan tertimbul (Peta yang diguna mempunyai 1,161,254 polygon). Berilah saya komputer jenis CPU quad-core dengan RAM 8GB dan mungkin saya boleh beri maklumbalas yang lebih positif.

Since it is possible to fit the Reprojected cadaster Map to Google Maps after a few hiccups, I assume the CPU, RAM and even graphic card may have something to do causing the initial inability of QGIS to put things properly because the more I zoom in, the more accurate the map. On the other hand, I do not know whether it could be because the file size is too big for QGIS to handle (That map has 1,161,254 polygon features). Give me a quad-core CPU with 8GB RAM and I may give you a more positive answer.

18/12/2012

QGIS Workshop by Harvard University


QGIS Workshop by Harvard University

This site by Lex Berman really gets my thumbs up and gives a clear set of tutorials. Presently, it covers:

  • Install
  • Basic
  • Import
  • Reproject
  • Join
  • Edit
  • Analyze
  • Symbolize
  • Export
  • Links
I particularly like the one on Reproject because I have faced much query on this. They even made an interesting observation that "NOTE: QGIS 1.8 has charset problems. We recommend using version 1.7.3 (Oct 2012)" Let's hope it expands further on.

16/12/2012

* How best to link QGIS to an internet server?


How best to link QGIS to an internet server?

Wrote something just now but am rethinking what was written especially to make it more layman understandable. Mmm... not as easy as I thought

10/12/2012

* Training: KKLW gets trained in QGIS





Latihan: KKLW mendapat latihan QGIS

Hari ini merupakan hari pertama bagi latihan QGIS untuk staf Bahagian Teknologi Maklumat dari Kementerian Luar Bandar dan Wilayah di Putrajaya. Ianya dihadiri oleh seramai 9 wanita yang lebih biasa dengan perisian GIS GeoMedia di Jabatan mereka akan tetapi berminat untuk mempelajari Quantum GIS. Tempo latihan bermula meningkat apabila mereka diberi peluang hands-on dalam menyediakan lapisan thematik masing-masing. Saya kerap menekankan bahawa yang penting adalah pengguna memahai prinsip disebalik GIS dari cuma menuruti langkah penceramah kerana apabila mereka tersangkut, ianya lebih mudah untuk mengatasi kesulitan yang dihadapi. Esok akan mereka belajar bab analisis seperti penggunaan SQL dan teknik untuk menggunakan modul-modul tertentu.

Training: KKLW gets trained in QGIS

Today is the first day of QGIS training for the IT Division of the Ministry of Rural and Regional Development at Putrajaya. It was attended by a team of 9 ladies who were mainly familar with the GIS software GeoMedia installed at their department but were keenly interest to learn Quantum GIS. As the day picked up, the tempo got exiting when they were given hands-on treatment at creating their own thematic layers. I always stressed that it was more important to understand the principle behind the steps in GIS than just following the trainer because when they got stuck, it would be easier to understand how to resolve the problem. Tomorrow they will concentrate on analysis such as SQl and the technique of using certain modules.

Norhaniza Abd Rahman

Taining yang mudah difahami dan senang digunakan. Now go for Open Source, jimat duit kerajaan

Siti Norhafizah Rosli
QGIS adalah software untuk GIS yang sangat bagus memandangkan function and properties yang terdpata dalam software ini adalah setanding denagn software berbayar yang lain. Recommended.

Noor Aziyan Ahmad Shah
QGIS neruopakan satu software yang mudah digunakan dan difahmai. Function yangt erdapt didialam QGIS adalah mudah dan clear. Memudahkan pengguna untuk plot peta dan dapatkan data-data yang diperlukan.

Norwahidah Wahid
QGIS software yang bagus dan setanding dengan software berbayar yang lain. Mempunyai fungsi dan atribut yang lebih kurang sama dengan software berbayar. mempunyai banyak reference bagi sesuatu isu sebab Open Source ma...

Zurina Hussein
Software yang mudah difahami dan digunakan. Boleh dipertimbangkan untuk kegunaan di Kementerian.

Farhana Ab Alim
Best angat belajar,s eronok, rugi kalo tak cuba. SOftware mudah difahami dan mudah dipelajari. Yang penting cikgu mengajar boleh buat gurau gurau :-D

Hadina Mohd Safri
Mudah dipelajari dan difahami walaupun pertama kali menggunakan perisian QGIS.

Asiah Abdul Rahman
Nampak mudah dan senang difahamai cuma perlu lebih latihan untuk lebih mahir.

Asnita Talsis
Open Source, jimat duit, simple, user-friendly

Resemas Edayu Mat Amin
Terima kasih


09/12/2012

Proprietary GIS Enemy No.1


Musuh utama GIS Berbayar

Pada asalnya, saya menyokong GIS berbayar kerana merupakan salah seorang pengguna. Bagaimana pun, sejak menjadi pengguna QGIS, sebagai kakitangan kerajaan, saya mendapati QGIS boleh membantu agensi awam yang memerlukan data GIS dalam merancang fizikal dengan berkesan akan tetapi mempunyai sumber kewangan terhad. Pernah saya berkhidmat di salah satu Majlis Daerah selama 3 tahun dan sedia maklum kebanyakkan Majlis Daerah mempunyai sumber kewangan terhad. Terdapat lebih kurang 150 pihak berkuasa tempatan di Malaysia dan 75% merupakan Majlis Daerah. Sebagai kakitangan kerajaan, saya ingin yang terbaik untuk perkhidmatan kerajaan dan sejak  2009 telah mempromosikan QGIS sebagai GIS utama bagi sektor awam. Oleh itu, tidak terkejutlah jika vendor GIS berbayar melihat saya seperti musuh ketatnya. Saya berpeluang bertemu dengan seorang perunding GIS berbayar di salah satu seminar GIS dan berkata jika situasinya terbalik, pasti akan saya mencari kelemahan-kelemahan GIS sumber terbuka kerana ianya menyulitkan keuntungan ataupun mencari niche dimana ianya dapat dieksploitasi. Pokoknya saya kakitangan kerajaan sehingga berpencen tidak lama lagi dan jika saya tidak mengambil langkah sebegitu, orang akan menyalahkan saya sebagai kakitangan kerajaan tidak beguna serta tidak mencari langkah-langkah untuk menjimatkan perbelanjaan kerajaan. Semalam, saya bertemu dengan bekas jururancang. Saya terangkan minat saya dalam OSS GIS dan berasa kekok mengenai perkara tersebut akan tetapi beliau berkata apa yang telah saya laksanakan sebagai kakitangan kerajaan adalah langkah yang baik dan betul. Tidak pernah saya berkata GIS berbayar tidak bagus. Saya cuma berkata cubalah OSS GIS dulu. Kalau ianya memenuhi kerperluan anda, alangkahnya baik di laburkan wang terhad dalam  infrastruktur ICT. Tetapi andai OSS GIS tidak memuaskan hati, pilihlah  GIS berbayar tapi suka tak suka terpaksalah sauadara keluarkan wang.

Proprietary GIS Enemy No.1

In my early days, I supported proprietary GIS since I too was a user. However, since becoming a QGIS user, as a humble government servant I found QGIS would benefit public agencies that depended on GIS data to effectively carry out physical planning yet lacked the financial resources. I too had the opportunity to work with a District Council (DC) for over 3 years and know only too well financial resource among DCs is limited. There are more than 150 local authorities throughout Malaysia and 75% of them are DCs. As a government officer, I do what is best for the government service and since 2009, I promoted QGIS as the principal GIS for the public sector. Still, I would not be surprised  proprietary GIS vendors see me as their Public Enemy No. 1. However, I have the chance to meet to a proprietary GIS consultant during a GIS seminar and explained that if I were on their side, I too would   be doing the opposite: finding flaws in Open Source GIS as it was not good for business or finding  a niche which I could exploit. But the fact  remains I am a government officer till I retire soon and if I were not doing what I am doing now, they would see me not as a good government officer trying his best to save government spending. Yesterday, I met a ex-planning officer. I explained my interest in OSS GIS and the awkward position I was in yet he too agreed as a government officer, I was doing a fine and right thing. I never said proprietary GIS is not good. I just said give OSS GIS a try, first. If it meets one's requirement why not use it and re-invest  limited funds on better ICT infrastructure. But if OSS GIS cannot meet one's requirement then acquire proprietary GIS though like it or not, it also means one has to folk out money.

08/12/2012

* Training: BCSS gets trained in QGIS




Latihan:  BCSS mendapat latihan QGIS

Barukini, the Biodiversity Conservation Society Sarawak (BCSS) telah memohon bantuan latihan QGIS maka ini merupakan sumbangan saya pada agensi non-profit organisation. Terdapat minat untuk mentransformasi data GPS data ke dalam bentuk spatial kerana ramai peserta ingin memplot pergerakkan binatang-binatang di Sarawak. Wow, kali ni penuh.


Training:  BCSS gets trained in QGIS

The Biodiversity Conservation Society Sarawak (BCSS) recently asked for help in getting training in QGIS so this became my contribution to a non-profit organisation. There was much interest in the transformation of GPS data into a spatial form as participants were keen in plotting out the migrationary pattern of animals in Sarawak. Wow, it was full house.

Hymeir Kamaruddin
Good intro to GIS for a beginner. Quantum GIS does the job well. Although I was looking at using GIS in the natural environemnt, learning using built environment is a good start. Good course and highly recommended.

Nurzhafarina Othman
Terima kasih

Lucy Peter
I think QGIS is user-friendly and a lot easier to understand (especially the tools usage) The availabiltity of free data (online) is another advantage of using this software. The only issues that I can see is sometimes there are plugins files which maybe corrupted which may cause inconvenience while working on a project. Overall this software is good!

Wong Ee Phin
I find QGIS very user-friendly. I hope the beginner training will help me to get started with QGIS. A good community and a growing network of users will help provide support to beginners. I hope to learn more.

Dylan Jefri Ong
Program yang bagus banyak perkara-perkara yang saya dapat pelajari. Mudah untuk difaham berbanding dengan ArcGIS . Saya suka...

Jii Ning
A very detail workshop but maybe it would be preferable if a clearer instruction given with a schedule of modules to go through prior to the workshop. Hopefully we can spend more time on the analysis part.

Jyunichi Washizaki
Terima kasih

Poh Tun Min
Terima kasih

Ashiegh Kivilaasko Seow
Terima kasih

Kae Kawanishi
Terima kasih

Wong Pui May
Terima kasih

John Mathal
Terima kasih

Nicholas Ong
First time getting to know about GIS and I find this is a very very useful tool. But would it be problematic when we use the Georeferencer in homogenous aerial photos? But all in all , this 2 days has been very good exposure!

Taha Wahab
This is my first time to use QGIS software in mapping. For the first day, quite difficult to get familiar with the software and in the second day, I find that the software is quite user-friendly as long as we know the function. My recommendation is if we can get the instruction manual to explain to the class the imortant points especially how to input the map tot he software etc. It is a good software and is free and hope I can use the software in my work.

Sim Lee Kheng
Terima kasih

Lim Wee Siong
As an introduction to GIS application, QGIS is good to get our handss on trying things out. Hope we will use more envronment management examples.

Jongkar Grinang
I never used any GIS software before. But I think QGIS does provide user-friendly features and is free of course. As this software is a free one, sharing inforamtion among the users is very helpful. The plugins modules would be very useful especially for the beginners

Felecity Anne Louise Oram
Terima kasih

Eddie Ahmad
Terima kasih

Su Li Khing
Terima kasih

(Participants forgot to mention name)
I think it's really good. Pretty user-friendly and free though it would help if the thing runs with less glitches.

Disyorkan selitkan contoh-contoh yang diberi dengan keperluan penonton. Contoh data mungkin boleh dipinjam daripada peserta atau daripada WCS sendiri sebagai penganjur.

05/12/2012

QGIS FAQ


Unlike the GIS FAQ, QGIS FAQ touches specifically on QGIS matters. It is my reference material based on personal experience as I stumble across things from queries which I embarrassingly could not answer due to plain ignorance or simply forgot or from complaints by others who blundered here and there while using QGIS but were too shy or have too much ego to admit it was them who did it (Yes I know, it's always the QGIS software, never them!). Just like the GIS FAQ, this article will be dynamic and updated from time to time.

How to move a node (point)?
Edit mode
A node or point is non-moveable until the active layer is set to edit mode. So firstly, select edit icon to set that layer to edit mode/click the preferred node until the red X changes into a red square/click the red square until it changes into a blue square/press cursor on blue square and move cursor to preferred location/select edit icon & save


Selectable mode

Moveable mode
How to re-activate the New Print Composer toolbar that went missing?

Place cursor on menu bar of New Print Composer/press the key in between 'Alt' and 'Ctrl' key/toolbar screen appears/tick all items on the toolbar to activate them 

How to print only a section of a map?

Zoom to a preferred section of the map only then activate the New Print Composer ('Add New Map' takes its image from image off the QGIS workscreen)

How to adjust the size of the map?

Firstly, resize the map by moving the cursor wheel. Alternatively, press Control key and move cursor wheel. Secondly, resize the frame of the map frame if necessary beyond the size of the paper. Thirdly, use 'Move item content' to readjust the location of the map. 

How to selectively delete an object on the digital paper?

Click in the region of a particular object frame until the 4 corners of its frame appear then press the delete button.

How to adjust the scale bar in the New Print Composer?

It is easiest to leave the default map units per bar unit to '1.00' then see the effect of changing the default segment size setting by typing '10', '100', '1000' or '10,000' or so then readjusting backwards if the scale bar exceeds the paper size. Some trial and error is required to find the correct fit against the preferred paper size.

How to save a layer to another format?
Alternative 1

If the intention is to save to a non-OGR format, activate a layer/under main menu/file/select save as image/select files of type/select preferred choice/ok
Alternative 2

If the intention is to save to an OGR format, activate a layer/ right-click mouse on layer in layer panel/select save as/select format/select preferred choice ok

What happens when I get a message like this from the Pyhton Plugin Installer?

That means the repository is down until a time the owner repairs it. Just click OK and carry on.

What happened to the 'Add 3rd party repositories' button?

It is only available in QGIS ver 1.7.5 and not in QGIS Ver. 1.8. This means the registeration of plugin repositories has to be manually done in QGIS Ver. 1.8.

How to re-activate Fetch Python Plugins?

Under menu bar/plugins/manage plugins/select 'Clear All'/OK


Under menu bar/plugins/manage plugins/select 'Select All'/OK (Fetch Python Plugins will re-appear)

How to  activate the North arrow or the scale bar?
In QGIS Ver. 1.7.5, both the North arrow and scale bar can be found under menu bar/plugins/decorations but in QGIS Ver. 1.8, it is found under menu bar/view/decorations.



By default, Enable Scale Bar is not ticked, thus, to activate it select 'Enable scale bar'.

How to make snapping options work?
The default size of the scale bar is 30metres/km. This scale does not show the snapping action well. Reduce that size to the minimum 1 meter/km and see the effect of the snapping action. If the snapping action is still minimal, adjust the tolerance unit proportionally to your map. This takes a bit of trial and error.

How to set the snapping options?

It is convenient and preferable in general to select the mode to 'vertex and segment' because there may be times when snapping action is required on both mode. The choice of tolerance value is subjective and relative to the scale the user decides. The user is required to do a few trial and errors between a fine setting such as 0.0001 and a coarse setting such as 0.1 only then will the user be able to compare and contrast which tolerance value is ideal.


It is preferable to select units in 'map units' rather than pixels because there is a natural tendency to make reference to snapping action base on what is seen on the canvas and not on the monitor.

How to change the default degree in the scale bar?

By default the scale bar is in degree, thus, to change it to meters or feet, selected the round icon at the bottom right corner of the QGIS workscreen/select General/select the preferred bullet e.g. meter or feet or degrees, minutes, seconds


How to make a plan that went missing to re-appear?

Under the Layer panel, right-click the layer map/select zoom to layer extent. (This causes the screen to 'jump' to the location where that plan has moved out of view.)

How to convert map projections?
Alternative 1:

Select menu bar/vector/data management tools/export to new projection/Decide between a predefined spatial reference system or import spatial reference from an existing layer/Create an output shapefile/OK

Alternative 2:

Under the Layer panel, right-click mouse on the preferred layer name/Decide between Layer CRS, Project CRS and Selected  CRS/Browse and decide between Geographic Coordinate Systems, Projected Coordinate Systems and  User Defined Coordinate System/Select 'Add saved file to map'/OK


Alternative 3:

Between 2 maps from the same Projected RS, the CRS of a properly projected map especially in the case where it refers to a User Defined System is copied and pasted onto the Parameter box of the map not properly aligned. Once copied, that map is saved to replace the original map. 'Zoom to layer' extent it to make it move to the location it ought to be.

Between 2 maps, one from a Geographic CR while the other from a Projected RS, I have yet to try this out as I do not have a sample with the former CRS so I can't answer this case... yet. 


How to get back the Layer panel?

Select menu bar/view/panels/ tick 'Layers'

How to link a database to QGIS?

Select menu bar/Layer/add vector/layer/select encoding e.g. system/ select database type e.g. PostgreSQL.


Select new/configure Connection information base on type e.g. PostgreSQL/Test Connect/OK/Open

Why an installed plugin does not get activated)?

After a 'not installed' plugin is installed, it does not necessarily mean that plugin was activated. To activate a particular plugin go to menu bar/plugins/manage plugins/tick the preferred plugin.


Why I cannot install QGIS to my Mac(kinstosh)?
It appears that when OSX Ver.1.6 upgraded to Ver 1.7, many engines that supported many games and applications including QGIS were taken out by Apple. Thus, those applications and games that worked well under Ver 1.6 now do not work . That seems to be the direction Apple has taken. (Commented by a friend who uses a Mac notebook and had QGIS successfully installed along with the plugins in manual mode in Ver 1.6 but QGIS cannot be installed when he upgraded to Ver.1.7)

What to do when a red line message appears when I try to activate Google Hybrid?

Quit QGIS/re-activate QGIS/re-activate Google Hybrid (It is suspected your cache is corrupted)

How to get rid of overlapping Globe menu?

For the time being, I think I have too many icons in the menu bar so when Globe was added, it overlap with others. Since I do not require it, Globe is unselect under 'Manage Plugins' and untick in the menu bar to clear it.

How to use a customize colour template?


Right-click a layer under the Layer panel/select properties/select load style/search & select your customized colour template e.g. plgcolour.qml/apply/ok

How to do I activate the missing "Join Attribute"?

Select menu bar/plugins/fetch python plugins/plugins/select ftools/select Downgrade plugin/close ('Join attibute' will appear under vector/data management tools)

How do I get rid of this message?

This screen will appear when QGIS is activated if the fTools was downgraded probably to take advantage of 'Join Attribute'. It will stay there so long as the installed fTools plugin is recognized by QGIS as technically obsolete because there is a newer version. If the installed fTools is upgraded, this message will be removed so the user must decide whether such features are important to oneself, no one else can decide that.

Why can't I find that .shp or .tab file?

Select menu bar/Layer/add vector layer/browse/select file type e.g. .shp or .tab /open (When browse screen was activated, if file type was '.tab' then only .tabs files will appear in the screen, vice versa) 

Which plugin should I download and install?
That depends on the user's requirement. Fundamentally, there are vector base plugins and raster base plugins for vector to suit a specific task. In QGIS Ver 1.8, when a raster base plugin is installed, it can be found under menu bar/raster whereas when a vector base plugin is installed, it can be found under menu bar/vector. Sometimes, there can be 2 vector headings under the menu bar, one for grouping vector base plugins and vector base tools so don't get confused.

How to re-activate the Georeferencer's GCP table toolbar that went missing?

Place cursor on menu bar of Georeferencer then right click mouse/tick items on the toolbar to activate them

How to re-do a georeference point that was badly done?

When a GeoReference point appears as a red line, it needs to be redone or else this will cause the image to be stretched when pasted later on the vector plan in accordance to the error as directed by the user.  To overcome this, place the cursor on the corresponding row in the GCP table under the on/off column, right-click the mouse/select 'remove' and that point disappears then repeat the georeferencing steps carried out earlier but this time with more accuracy and precision.


How to add diagrams?
Alternative 1

Right-click cursor on active layer under Layer Panel/properties/diagrams/select display diagram/select preferred diagram type/configure respective settings/ok


Alternative 2

Right-click cursor on active layer under Layer Panel/properties/overlay/select display diagram/select preferred diagram type/configure respective settings/ok


How to do away with on-the-fly projection?
On-the-fly projection interferes with a preferred map projection as it overrides it. To have control of over a preferred map projection, on-the-fly projection needs to be unselected. 
Alternative 1

Under menu bar/setting/options/CRS/unselect  'Enable on-the-fly reprojection by default'/OK

Alternative 2

Select the round icon at the bottom right corner of the QGIS workscreen/select Coordinate reference System (CRS)/ unselect Enable 'on-the-fly' CRS transformation/OK


How to do label features?
Alternative 1

Right-click cursor of active layer under Layer Panel/properties/labels/select 'Display labels'/Under label properties, select preferred 'field containing label'/configure respective label properties setting/OK


Alternative 2
Under menu bar, select labeling icon/select 'Label this layer with'/select preferred field/configure label settings/OK


How to ensure spelling correction works?
If the user jumps straight into the task of correcting spelling errors with the field calculator base on the appropriate procedure in the filed calculator be surprised because nothing happens. That is because QGIS was not taught which feature to correct and that requires a prior step to identify the required features using the SQL query after which all will turn out well.



How to calculate in hectares?
In the field calculator, use the 'area' operator where the expression is $area but add "/10000" to convert metre to hectare. The final result only appears after the file has been SAVED!


How to calculate the SUM of something?
'SUM' is a statistical function. Therefore, the total of a specific listing in an attribute table can be obtained by using the Basic Statistics module under Vector/Analysis Tools. Select appropriate layer/  select the appropriate column/Select OK.