Laying the foundation

ONE WAY, NOT THE ONLY WAY

QGIS usually offers several ways to do the same task: a processing algorithm, the Field Calculator, a plugin, or editing by hand. The steps in this module are examples of how to do each task, tested with the course’s sample data. They are not the only way, and other methods are equally valid as long as the outputs meet the guide’s requirements and agree with each other. Where a choice affects correctness (for example, using area($geometry) instead of $area), the module says why.

Introduction

This module introduces the requirements of the Guide for the Standard Mapping (FMB Memorandum dated 15 February 2024) for forestry tenure applications such as SFLMA, and the coordinate reference systems you need to meet them. Everything in the later modules builds on these two topics.

What you should already know

Familiarity with the QGIS interface as discussed in QGIS: Essentials - Introduction to QGIS, how to load different kinds of layers as discussed in QGIS: Essentials - Introduction to layers in QGIS, and the basics of map projections and coordinate reference systems as discussed in QGIS: Essentials - Introduction to geospatial concepts are preferred.

What the standard mapping guide requires

LEARNING OBJECTIVES

1. Identify the four digital outputs required for a forestry tenure application.
2. Understand why the four outputs must agree with each other.
3. Apply the prescribed naming formats for shapefiles and technical descriptions.

The four required outputs

Every forestry tenure application is submitted with four digital outputs. Each one is covered by a module in this course.

Output	Format	Covered in
Map of the subject area with the appropriate signatories of the concerned offices, company, or applicant	Map (prescribed layout)	The prescribed map layout
Shapefiles of the area’s corners (point) and boundary (polygon) with the prescribed attributes	Shapefile (.shp)	Preparing the area data
Technical description in the standard bearing-distance format, with the description of the tie point and tie line used	Spreadsheet (.xls)	Technical descriptions and corner coordinates
Computed coordinates of the corners	Comma-separated values (.csv)	Technical descriptions and corner coordinates

One area, four views

The four outputs are not four separate tasks. They are four views of the same area: the corners in the point shapefile are the corners in the technical description, the polygon is the area on the map, and the area on the map is the area in the attribute table.

IMPORTANT!

Most returned applications fail on agreement, not on any single output: a technical description that does not close, an area that differs between the map and the attribute table, or corner coordinates that do not match the shapefile. This is why the course ends with cross-validation and quality control.

Naming formats

The guide prescribes the following file names:

File	Format
Shapefiles (.shp)	<Region>_<Tenure Type>_<Point or Polygon>_<Applicant's Name>
Technical description and computed coordinates (.xls or .csv)	TD_<Region>_<Tenure Type>_<Applicant's Name>

If the application involves multiple parcels:

• the technical descriptions and coordinates of each parcel are kept in separate sheets or tabs,
• each parcel has its own point shapefile, and
• all parcels share only one polygon shapefile.

For the sample application in this course, the files are:

IV-A_SFLMA_Point_Bagong Gubat Agroforestry Cooperative.shp   (with .dbf, .shx, .prj, .cpg)
IV-A_SFLMA_Polygon_Bagong Gubat Agroforestry Cooperative.shp (with .dbf, .shx, .prj, .cpg)
TD_IV-A_SFLMA_Bagong Gubat Agroforestry Cooperative.xlsx
TD_IV-A_SFLMA_Bagong Gubat Agroforestry Cooperative.csv

Shapefiles for submission, GeoPackage for your work

LEARNING OBJECTIVES

1. Know the limits of the shapefile format that matter for tenure mapping.
2. Keep working data in a GeoPackage and produce shapefiles only for submission.

The guide requires shapefiles, and the submitted files must be shapefiles. That does not make the shapefile a good format to work in. In this course, the shapefile limits show up in the tenure workflow itself:

Shapefile limit	Where it shows up in this course
Field names are cut to 10 characters	The tie line’s fields TIE_DISTANCE and TIE_BEARING would become TIE_DISTAN and TIE_BEARIN, and REFERENCE_POINT would become REFERENCE_
Text fields hold at most 254 characters	The guide’s Length: 255 becomes 254 (Module 2)
Field names ignore upper and lower case	A new field x collides with the prescribed X, so QGIS names it x_2 (Module 3)
One shapefile is several files (.shp, .shx, .dbf, .prj, .cpg)	Send or upload the files without the .prj, and the layer opens with no CRS
One layer per file	One application already needs two shapefiles, plus the technical description lines, tie point, reference layers, and project kept elsewhere

A GeoPackage (.gpkg) is a single file that holds many layers, with long field names and no 254-character limit, and it can also store the QGIS project. In this course, the working layers (the technical description lines, the tie point, the reference layers, and the project) live in GeoPackages, and only the two submission layers are shapefiles, created with the prescribed fields from the start.

PRO-TIP

Keep each application’s working data in its own GeoPackage, and treat the shapefiles as an export for submission. If you ever need to rebuild the shapefiles, you can export them again from the GeoPackage.

Read more in QGIS: Essentials - A quick note about shapefiles.

Coordinate reference systems for tenure mapping

LEARNING OBJECTIVES

1. Differentiate the Luzon 1911 and PRS 1992 datums.
2. Identify the correct national grid zone for an area.
3. Set the correct CRS for a forestry tenure project in QGIS.
4. Understand why data must not be converted between Luzon 1911 and PRS 1992 in QGIS.

The guide requires that the shapefiles of the corners and the boundary be projected using Luzon 1911 or PRS 1992 using the national grids.

Luzon 1911 and PRS 1992

Luzon 1911 and the Philippine Reference System of 1992 (PRS 1992) are two geodetic datums used in the Philippines. Both use the Clarke 1866 ellipsoid, but they are not the same: the same point on the ground has different coordinates in each datum.

Older survey records and many reference monuments (e.g. BLLMs) carry Luzon 1911 coordinates, while newer records use PRS 1992. The datum you use is decided by the technical description and its tie point, not by preference.

The national grid (Philippine Transverse Mercator zones)

The national grid divides the country into five zones, each two degrees of longitude wide and centred on its own central meridian. Both datums use the same zones, so each zone has two CRSs in QGIS.

Zone	Central meridian	Luzon 1911	PRS 1992
I	117° E	EPSG:25391	EPSG:3121
II	119° E	EPSG:25392	EPSG:3122
III	121° E	EPSG:25393	EPSG:3123
IV	123° E	EPSG:25394	EPSG:3124
V	125° E	EPSG:25395	EPSG:3125

All ten use a transverse Mercator projection with a scale factor of 0.99995 and a false easting of 500,000 m.

PRO-TIP

The technical description usually names its zone and datum (e.g. Luzon Zone III or PRS 1992 Philippines Zone III). If it does not, the zone is the one whose central meridian is nearest the area’s longitude.

NOT UTM

The national grid is not UTM. Coordinates in UTM zone 51N (e.g. EPSG:32651) look similar in magnitude but are on a different projection, so they are not interchangeable with national grid coordinates.

Don’t convert between Luzon 1911 and PRS 1992

QGIS can reproject between the two datums, but the result is not survey-grade, and it depends on which transformation QGIS uses. At the sample application’s corner 1 in General Nakar, the same coordinates read as Luzon 1911 instead of PRS 1992 land:

Transformation QGIS uses	Rated accuracy	Shift at corner 1
Luzon 1911 to WGS 84 (1), the default	17 m	7.7 m
Luzon 1911 to WGS 84 (2)	44 m	22.6 m
Ballpark geographic offset	none	0 m

The sample application’s corners read as PRS 1992 Zone III (red) and as Luzon 1911 Zone III (blue): 7.7 m apart at corner 1

IMPORTANT!

Keep the shapefiles, the technical description, and the tie point in the same datum and zone as the technical description. Do not reproject an application area between Luzon 1911 and PRS 1992 to “fix” a mismatch: get the tie point coordinates in the correct datum instead.

1.1. Setting up a forestry tenure project

Level: Beginner

What we want to achieve

• A QGIS project set to the datum and zone of the sample application’s technical description, ready for the exercises in the next modules.

What we have

• bnhr_qgis-sflma-mapping-001.gpkg inside the data subfolder of the BNHR_QGIS-for-SFLMA-Mapping folder.
• The sample technical description, which states its datum and zone.

1. Read the sample technical description and identify its datum and zone. The sample application uses PRS 1992 Philippines Zone III.
2. Open Project ‣ Properties ‣ CRS. Type Philippines zone in the Filter box to list the national grid CRSs, then select PRS92 / Philippines zone 3 (EPSG:3123).

Filtering for the national grid CRSs and selecting PRS92 / Philippines zone 3

3. Open Project ‣ Properties ‣ Transformations. When the list is empty, QGIS picks a transformation automatically whenever layers in other datums are loaded.

Datum transformations in the Project Properties

4. Load ref_barangays, ref_municipalities, ref_provinces, and sample_tie_point from bnhr_qgis-sflma-mapping-001.gpkg and check the CRS of each one in Layer Properties ‣ Information. All of them are in EPSG:3123.

The barangays of General Nakar and the sample tie point, in PRS92 / Philippines zone 3

5. Save the project (Project ‣ Save To ‣ GeoPackage) inside the GeoPackage so that the project and data travel together.

THE PROJECT CRS ALSO SETS THE ELLIPSOID

Setting the project CRS to a national grid CRS also sets the project’s ellipsoid to Clarke 1866. This matters for areas and distances computed with $area and $length; see Computing the area and location attributes.

TRY FOR YOURSELF

Load a layer in a different datum. What does QGIS ask you? What happens to the layer’s position if you accept the default transformation?

Beyond files: managing applications as data

Every application the office prepares or reviews adds a set of files: two shapefiles, a technical description, a coordinate file, and a map. Each check in Cross-validation and quality control, such as overlaps with existing tenures, is only as good as the reference data it is run against, and that reference grows with every approved application.

When the files of many applications are scattered across folders and upload links, it becomes hard to answer questions like which approved tenures does this application overlap? or which applications are in this barangay?, or to let several staff work on the same data at once. These are data management problems:

• a spatial database (PostGIS) that keeps every application and tenure in one place, checked with the same rules, and shared by several users;
• web services (GeoServer, OGC APIs) that let field offices view and use the same layers without copying files; and
• a catalogue (GeoNode) that makes the office’s maps and data searchable.

We teach these in Geospatial Data Management & Engineering with BNHR, from storing spatial data in PostGIS to sharing it with GeoServer and cataloguing it with GeoNode.

The bare minimum QGIS knowledge

Must-haves

Map projections and Coordinate Reference Systems

• What’s the difference between geographic and projected CRS?
• How do you change the CRS of a project in QGIS?
• How do you change the CRS (reproject) of a layer in QGIS, and when should you not do it?

Working with attributes

• How do you open and edit the attribute table?
• How do you use the Field Calculator?

Creating and editing layers

• How do you create a new vector layer?
• How do you digitize with snapping and the advanced digitizing panel?

The Print Layout

• How do you add a map, legend, scale bar, and north arrow to a layout?
• How do you save and open a layout template?

Certification and support

LOOKING FOR CERTIFICATION AND SUPPORT?

We offer additional resources, certificates, official QGIS certification, ongoing support, and other perks to those who join our instructor-led training.

Join an upcoming training to take this as an instructor-led course, or contact us to arrange one for your team or organization.