> For the complete documentation index, see [llms.txt](https://codifi-fdm.gitbook.io/codifi-docs/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://codifi-fdm.gitbook.io/codifi-docs/mobile-app/mapping-locations/before-you-head-to-the-field.md).

# Before You Head to the Field

A few minutes of preparation can save you hours of frustration in the field. Here's your pre-departure checklist:

#### Download Your Offline Maps

**Why it matters:** Without pre-downloaded maps, you'll see a blank screen (no base layer) in areas without cell service. If you view the map online, the base imagery or data may cache on your device for the specific map tiles you viewed, and will persist when offline for a period of time, but this shouldn't be relied on. Use the Offline Maps if you are deploying into areas with low/no signal!

{% hint style="warning" %}
**Prerequisite**: A Project Admin with access to your Project on the Codifi Web App need to designate one or more Offline Map Areas in the Project's settings. This cannot be done through the mobile app.
{% endhint %}

How to download designated Offline Map Areas:

1. Open the Codifi app while you still have WiFi or good cell service
2. Navigate to your Project and switch to Map View
3. Tap the Layers button (stacked squares icon, top-right of map)
4. In the Overlays section, find "Offline Areas" and toggle it ON
5. Tap the icon next to Offline Areas to see available download regions
6. Wait for downloads to complete

<figure><img src="https://3544178300-files.gitbook.io/~/files/v0/b/gitbook-x-prod.appspot.com/o/spaces%2FJ8P3pqhxdFwQkIOjOUut%2Fuploads%2FWUlCDYNS5HOqa8d0fvAJ%2Fezgif.com-video-to-gif-converter.gif?alt=media&amp;token=2cc05bda-c47f-40ab-8e10-5944fe579bdc" alt=""><figcaption></figcaption></figure>

{% hint style="info" %}
**Tip**: You can close the Layers sheet and keep working while maps download in the background.
{% endhint %}

#### Connect Your External GPS (If Using One)

If you've been given an external GPS receiver (a Trimble unit, an Emlid Reach, a Bad Elf, or another Bluetooth GPS), test connect it before you leave. See [External GPS Devices](/codifi-docs/mobile-app/mapping-locations/external-gps-devices.md) for the pairing flow for each type.

**To access External Devices:**

1. Tap anywhere on the **GPS source label** in the Live Data Bar (shows "iPad GPS" or device name)
2. The **External Devices** panel opens

**For Trimble devices:**

1. In the External Devices panel, tap the **+ button**
2. Select **"Trimble Device"**
3. Tap **"Open TMM"** (Trimble Mobile Manager) and pair your device there
4. Return to Codifi — your Trimble should appear in Connected Devices

**For Bluetooth (BLE) GPS receivers:**

1. Turn on your GPS receiver and enable Bluetooth on your iPad/iPhone
2. In the External Devices panel, tap the **+ button**
3. Select **"BLE Device"**
4. Tap **"Scan"** — available devices will appear
5. Tap **"Connect"** next to your device

**For MFi (Made for iPhone/iPad) devices:**

1. In the External Devices panel, tap the **+ button**
2. Select **"MFi Device"**
3. Tap **"Open iOS Settings"** to pair via Bluetooth Settings

<figure><img src="https://3544178300-files.gitbook.io/~/files/v0/b/gitbook-x-prod.appspot.com/o/spaces%2FJ8P3pqhxdFwQkIOjOUut%2Fuploads%2FIXRyT1B7ak9HzAS6bRTF%2FScreenRecording_01-08-202610-30-08_1-ezgif.com-video-to-gif-converter.gif?alt=media&amp;token=15a7cda4-f167-4528-afec-2746af41f3d2" alt=""><figcaption></figcaption></figure>

{% hint style="info" %}
**How do you know it's working?** The GPS source name in the Live Data Bar should show your device name (like "Trimble R2", "Bad Elf GPS", etc.) instead of "iPad GPS".
{% endhint %}

#### Setting Your Favorite GPS

Once connected, set your preferred GPS as the default:

1. In the External Devices panel, find your device in the list
2. Tap anywhere on the device row to open options
3. Select **"Use as Favorite GPS"**

The device marked as favorite will have a star icon and highlighted styling. The app remembers your preference and will automatically use your favorite GPS when it's connected.

#### Charge Your Devices

GPS usage drains batteries quickly. Make sure both your iPad/iPhone and any external GPS receivers are fully charged. Bring a portable battery pack if you'll be out all day.<br>